Semiconductor device and method of manufacturing the semiconductor device

ABSTRACT

An active region in a semiconductor device is made up of a parallel p-n layer including a first p-semiconductor layer and a first n-semiconductor with the widths and total amounts of impurities being equal to each other to provide a structure in which charges are balanced. A section parallel to stripes in the parallel p-n layer in an inactive region is made up of a second parallel p-n layer including a second p-semiconductor layer, with its width larger than that of the first p-semiconductor layer, and a second n-semiconductor layer with its width smaller than that of the first n-semiconductor layer. The total amount of impurities in the second p-semiconductor layer is made larger than that in the second n-semiconductor layer to provide a structure in which charges are made unbalanced.

This is a divisional application of U.S. patent application Ser. No.11/054,366 filed on Feb. 9, 2005

BACKGROUND OF THE INVENTION

The present invention relates to a semiconductor device having in adrift section a parallel p-n layer arranged with n-type semiconductorlayers and p-type semiconductor layers being alternately joined and amethod of manufacturing the semiconductor device having such anarrangement.

In general, semiconductor elements may be classified into lateralelements each having electrodes formed on its one side and verticalelements each having electrodes on both sides. In a vertical element,both of the direction in which a drift current flows in a turned-onstate and the direction in which a depletion layer, formed by a reversebias voltage, extends in a turned-off state are the same. In an ordinaryplaner n-channel vertical MOSFET (insulated gate field effecttransistor), a high resistance drift layer is operated as a region forflowing a drift current in the vertical direction when the MOSFET is ina turned-on state. Therefore, a shortened current path in the driftlayer lowers drift resistance, by which an effect of reducingsubstantial on-resistance of the MOSFET is obtained.

While, the drift layer is depleted when in a turned-off state to enhancea breakdown voltage. Therefore, the thinned drift region narrows theexpanding width of a depletion layer between the drain and the basewhich layer travels from the p-n junction between a p-type base regionand the n-type drift layer. This causes the electric field strength inthe depletion layer to fast reach the critical electric field strengthof silicon to lower the breakdown voltage. Contrary to this, in asemiconductor element with a high breakdown voltage, a thick drift layerincreases on-resistance to result in an increase in a loss. In this way,between the on-resistance and the breakdown voltage, there is a relationthat necessitates a tradeoff.

The tradeoff is known to be similarly necessary also in a semiconductorelement such as an IGBT (insulated gate bipolar transistor), a bipolartransistor or a diode. Moreover, the same tradeoff is necessary also ina lateral semiconductor element in which the direction in which a driftcurrent flows in a turned-on state differs from the direction in which adepletion layer extends in a turned-off state.

A well-known solving measure to the problem of necessitating theabove-explained tradeoff is to provide a super-junction semiconductorelement in which a drift layer is provided as a parallel p-n layerhaving a structure with n-type semiconductor layers and p-typesemiconductor layers alternately joined, both having increased impurityconcentrations. In the semiconductor device with such a structure, eventhough the impurity concentrations in the parallel pn-structure arehigh, when in a turned-off state, a depletion layer expands in thelateral direction from each p-n junction extending in the verticaldirection of the parallel p-n layer. This makes the whole drift sectiondepleted, by which a high breakdown voltage can be provided.

A previously known method of making a parallel p-n layer of asuper-junction semiconductor device is a method of alternately carryingout epitaxial growth of the n-type semiconductor layer and selective ionimplantation of p-type impurities (hereinafter referred to as amultistage epitaxial growth method). The method is disclosed in, forexample, JP-A-2001-298190 and JP-A-2003-224273. Another method isproposed in JP-A-2001-196573, for example, in which a plurality oftrenches are formed in an n-type semiconductor layer and each trench isfilled with an epitaxial layer of p-type semiconductor (hereinafterreferred to as a trench filling method).

In the trench filling method, the number of times of carrying out theepitaxial growth is smaller than that in the multistage epitaxial growthmethod. This provides the advantage of lowering cost. However, forensuring a breakdown voltage of a super-junction semiconductor devicemanufactured by the trench filling method, a peripheral voltagewithstanding structure, provided in an edge structure section, must bemade different from the structure provided in the case when thesuper-junction semiconductor device is manufactured by the multistageepitaxial growth method. Here, the edge structure section is provided inthe inactive region on the outside of the active region in which acurrent flows when the super-junction semiconductor device is in aturned-on state.

The reason will be explained in the following. Here, all of the MOSFETsare taken as those of n-channel type. Moreover, the parallel p-n layeris taken as a structure with a plane figure in which long narrowextended n-semiconductor layers and p-semiconductor layers arealternately joined in the direction perpendicular to the extendingdirection of the n-semiconductor layers (hereinafter referred to as astripe-pattern-like plane figure). In the specification, the directionin which the n-semiconductor layer (or the p-semiconductor layer) in theparallel p-n layer are extended is taken as the direction parallel tothe stripes in the parallel p-n layer. The direction orthogonal to thisis taken as the direction perpendicular to the stripes in the parallelp-n layer.

Moreover, it is assumed that, in the inactive region, there are laid outa parallel p-n layer with a high impurity concentration like theparallel p-n layer in the active region. A section along a sideextending in the direction perpendicular to the stripes of the parallelp-n layer in the edge structure section becomes a lateral super-junctionstructure when the MOSFET is in a turned-off state, which can ensure asufficiently high breakdown voltage in the section. Meanwhile, in asection along a side extending in the direction parallel to the stripesof the parallel p-n layer in the edge structure section, a depletionlayer tends to expand in the horizontal direction (lateral direction)from the p-n junctions when the MOSFET is in a turned-off state. Thedepletion layer, however, is not made to expand sufficiently because ofhigh impurity concentration in the n-semiconductor layer in the parallelp-n layer laid out in the inactive region. Therefore, a sufficientlyhigh breakdown voltage cannot be ensured in the edge structure sectionparallel to the stripes.

In order to avoid the problem, it is necessary to provide the structureof the parallel p-n layer in the edge structure section as a structuredifferent from the structure of the parallel p-n layer in the activeregion. That is, the structure must be provided as a structure thatreduces the electric field strength at least on the surface of theparallel p-n layer in the edge structure section to make a depletionlayer expand easily in the edge structure section. Specifically, such astructure is disclosed in the above JP-A-2001-298190 as a structure inwhich, in the parallel p-n layer in the edge structure section, impurityconcentration is lowered or the pitch of the stripes is narrowed.Furthermore, the impurity concentration is lowered together with thepitch of the stripes is narrowed or the impurity concentration islowered together with the pitch of the stripes is increased. In thestructure disclosed in the above JP-A-2001-298190, as shown in FIG. 47,in the parallel p-n layer in the active region, the amounts ofimpurities in the p-semiconductor layer and that in the n-semiconductorlayer are equal to each other. Moreover, in the edge structure section,that is, in the parallel p-n layer in the inactive section, the amountsof impurities in the p-semiconductor layer and that in then-semiconductor layer are also equal to each other.

In the above JP-A-2003-224273, a structure is disclosed in which theparallel p-n layer in the edge structure section is divided into twolayers, an upper layer section and a lower layer section. In thestructure, only in the parallel p-n layer in the upper layer section,impurity concentration is lowered or the pitch of the stripes isnarrowed. Furthermore, the impurity concentration is lowered togetherwith the pitch of the stripes is narrowed or the impurity concentrationis lowered together with the pitch of the stripes is increased. Thesuper-junction semiconductor devices disclosed in the aboveJP-A-2001-298190 and JP-A-2003-224273, are manufactured by themultistage epitaxial growth method. In the multistage epitaxial growthmethod, by changing a dose at selective ion implantation and/or a ratioof a window width at ion implantation, impurity concentration can bechanged. Therefore, it is easy to lower only the impurity concentrationin the parallel p-n layer in the edge structure section.

In general, for ensuring a stable breakdown voltage in a semiconductordevice, a peripheral voltage withstanding structure must be provided.However, in the above JP-A-2001-196573 in which the trench fillingmethod is proposed, no peripheral voltage withstanding structure and nomethod of manufacturing the structure are mentioned. Thus, the deviceaccording to the above JP-A-2001-196573 has a possibility of making itdifficult to ensure a stable breakdown voltage. Therefore, the inventorsstudied the technique of forming the peripheral voltage withstandingstructure as is disclosed in the above JP-A-2001-298190 by the trenchfilling method as is disclosed in the above JP-A-2001-196573. As aresult, it was found that the widths of the p-semiconductor layers andthe n-semiconductor layers in the parallel p-n layer can be controlledby changing the width of each of the trenches to be formed and spacingbetween the trenches (pitch). Specifically, it was found that, forensuring the stable breakdown voltage, it is only necessary to make thewidths and the pitch of the trenches in the inactive region smaller thanthe widths and the pitch of the trenches in the active region.

However, the trench widths in the inactive region made excessive smallcause too low impurity concentrations in the p-semiconductor layers.This results in weakened effect of expanding the depletion layer outwardthe p-semiconductor layers. Therefore, the depletion layer expandspoorly to cause inconvenience of making the breakdown voltage hard to beensured. Moreover, trench widths made excessively small in the inactiveregion cause the trenches hard to be formed. Along with this, an aspectratio of each of the trenches is made too high to cause difficulty infilling the trenches with epitaxial layers.

In addition, there was also studied the technology of forming theperipheral voltage withstanding structure as is disclosed in the aboveJP-A-2003-224273 by the trench filling method. In the disclosedstructure, the parallel pn-structure in the edge structure section inthe inactive region is divided into two layers of the upper layersection and the lower layer section. As a result, it was found that tochange impurity concentration only in the p-semiconductor layer in theupper layer section or only in the n-semiconductor layer in the upperlayer is impossible with one time formation of the trenches and one timeepitaxial growth for filling the trenches. This is attributed to uniformdistribution of the impurity concentration in the substrate before thetrenches are formed therein and impurity concentration distributionbecoming uniform when the trenches are filled.

The invention was made in view of the foregoing with an object ofproviding a semiconductor device being provided with a super-junctionstructure capable of ensuring a sufficiently high breakdown voltage.Another object of the invention is to provide a semiconductor deviceprovided with a super-junction structure suited for being manufacturedby a trench filling method. Further another object of the invention isto provide a method of manufacturing a semiconductor device providedwith the super-junction structure by the trench filling method.

SUMMARY OF THE INVENTION

In order to achieve the above object, a semiconductor device accordingto a first aspect of the invention is a device in which a parallel p-nlayer with first conductivity type semiconductor layers and secondconductivity type semiconductor layers being alternately joined isprovided on a first conductivity type low resistance semiconductor layerand the parallel p-n layer is laid out both in an active region in whicha current flows in a turned-on state and in an inactive region aroundthe active region, wherein in at least a part of the parallel p-n layerlaid out in the inactive region, the total amount of impurities in thesecond conductivity type semiconductor layer is larger than the totalamount of impurities in the first conductivity type semiconductor layer.

According to the first aspect of the invention, in the inactive region,although charges in the parallel p-n layer are made unbalanced, theimpurities of a larger total amount in the second conductivity typesemiconductor layer in the parallel p-n layer enhance the depletion inthe first conductivity type semiconductor layer in the outer peripheralsection of the second conductivity type semiconductor layer. Moreover,in the inactive region, the lowered impurity concentration in the firstconductivity type semiconductor layer enhances depletion in the firstconductivity type semiconductor layer. This reduces the electric fieldstrength in the inactive region, so that a sufficiently high breakdownvoltage can be ensured.

A semiconductor device according to a second aspect of the invention isa device in which, in the device according to the first aspect of theinvention, in at least a part of the parallel p-n layer laid out in theinactive region, the width of the second conductivity type semiconductorlayer is larger than the width of the first conductivity typesemiconductor layer.

According to the second aspect of the invention, in at least a part ofthe parallel p-n layer laid out in the inactive region, interdiffusionof impurities between the first conductivity type semiconductor layerand the second conductivity type semiconductor layer increases the totalamount of impurities in the second conductivity type semiconductor layerto be larger than that in the first conductivity type semiconductorlayer. Realization of the structure according to the second aspect ismade possible by the following. First, a first conductivity typesemiconductor layer is formed on the first conductivity type lowresistance semiconductor layer. Then, a plurality of trenches are formedin at least a part of the region to become the inactive region in thefirst conductivity type semiconductor layer so that the width of each ofthe trenches becomes larger than the width of the first conductivitytype semiconductor layer between the trenches. Finally, each of thetrenches is filled with an epitaxially grown second conductivity typesemiconductor layer. Therefore, the structure is suited for being formedby the trench filling method.

A semiconductor device according to a third aspect of the invention is adevice in which, in the device according to the second aspect of theinvention, the width of the second conductivity type semiconductor layerin the parallel p-n layer laid out in the inactive region is equal tothe width of the second conductivity type semiconductor layer in theparallel p-n layer laid out in the active region.

According to the third aspect of the invention, in the region to becomethe inactive region, the width of the trench for forming the secondconductivity type semiconductor layer in the parallel p-n layer aresimply made to be equal to the width of the trench formed in the regionto become the active region. Hence, an aspect ratio of the trench formedin the region to become the inactive region can be determined to such anextent that the trench can be formed and the trench can be filled withan epitaxially grown semiconductor layer. Therefore, the structure issuited for being formed by the trench filling method.

A semiconductor device according to a fourth aspect of the invention isa device in which, in the device according to the second aspect of theinvention, in at least a part of the parallel p-n layer laid out in theinactive region, the width of the second conductivity type semiconductorlayer is larger than the width of the second conductivity typesemiconductor layer in the parallel p-n layer laid out in the activeregion.

According to the fourth aspect of the invention, in at least a part ofthe region to become the inactive region, the width of the trench forforming the second conductivity type semiconductor layer in the parallelp-n layer are simply made larger than the width of the trench formed inthe region to become the active region. Hence, an aspect ratio of thetrench formed in at least a part of the region to become the inactiveregion can be determined to such an extent that the trench can be formedand the trench can be filled with an epitaxially grown semiconductorlayer. Therefore, the structure is suited for being formed by the trenchfilling method.

A semiconductor device according to a fifth aspect of the invention is adevice in which, in the device according to the first aspect of theinvention, in at least a part of the parallel p-n layer laid out in theinactive region, the widths of the first conductivity type semiconductorlayer and the second conductivity type semiconductor layer are smallerthan the widths of the first conductivity type semiconductor layer andthe second conductivity type semiconductor layer in the parallel p-nlayer laid out in the active region, respectively.

According to the fifth aspect of the invention, in at least a part ofthe region to become the inactive region, the width and the pitch of thetrench for forming the second conductivity type semiconductor layer inthe parallel p-n layer are simply made smaller than the width and thepitch of the trench formed in the region to become the active region,respectively. Hence, by determining the aspect ratio of the trench,formed in at least a part of the region to become the inactive region,to such an extent that the trench can be formed and the trench can befilled with an epitaxially grown semiconductor layer, a structure isprovided which is suited for being formed by the trench filling method.In the semiconductor device according to the fifth aspect of theinvention, in at least a part of the parallel p-n layer laid out in theinactive region, the width of the first conductivity type semiconductorlayer is better made smaller than that of the second conductivity typesemiconductor layer.

In order to achieve the above object, a method of manufacturing asemiconductor device according to a sixth aspect of the invention is themethod which, when manufacturing a semiconductor device in which aparallel p-n layer with first conductivity type semiconductor layers andsecond conductivity type semiconductor layers being alternately joinedis provided on a first conductivity type low resistance semiconductorlayer and the parallel p-n layer is laid out both in an active region inwhich a current flows in a turned-on state and in an inactive regionaround the active region, includes the steps of: carrying out epitaxialgrowth of a first conductivity type semiconductor layer on the firstconductivity type low resistance semiconductor layer; depositing aninsulator film on the surface of the epitaxially grown firstconductivity type semiconductor layer; carrying out patterning of theinsulator film to form a mask for forming trenches; by using thepatterned insulator film as a mask, forming a plurality of trenches in aregion to become an active region in the first conductivity typesemiconductor layer and along with this, forming a plurality of trenchesin a part of a region to become an inactive region in the firstconductivity type semiconductor layer, the trenches having widthsdifferent from those of the trenches formed in the region to become theactive region; carrying out epitaxial growth of a second conductivitytype semiconductor layer in each of the trenches formed in the firstconductivity type semiconductor layer to fill trenches having thelargest widths with the second conductivity type semiconductor layers toa level equal to or higher than the level of the surface of theinsulator film used as the mask for forming the trenches; and polishingthe parallel p-n layer comprising the first conductivity typesemiconductor layers and the second conductivity type semiconductorlayers filling the trenches to planarize the surface of the parallel p-nlayer.

According to the sixth aspect of the invention, in a part of theparallel p-n layer laid out in the inactive region, there can be formedsecond conductivity type semiconductor layers having widths differentfrom those of the second conductivity type semiconductor layers in theparallel p-n layer laid out in the active region. Therefore, the totalamount of impurities in the second conductivity type semiconductor layerin the parallel p-n layer in the inactive region is made increased to belarger than the total amount of impurities in the first conductivitytype semiconductor layer. This enhances depletion in the inactive regionto reduce the electric field strength in the inactive region, by which asemiconductor device can be obtained which is capable of ensuring asufficiently high breakdown voltage. Moreover, by filling the trencheshaving the largest widths with the second conductivity typesemiconductor layers under an over-epitaxial condition, trenches havingdifferent widths from one another can be filled by a single step offorming the trenches and a single step of filling the trenches.

A method of manufacturing a semiconductor device according to a seventhaspect of the invention is a method in which, in the method according tothe sixth aspect of the invention, in the step of forming the trenchesin the first conductivity type semiconductor layer, in a part of theregion to become the inactive region, the trenches are formed so thatthe width of each of the trenches becomes larger than the spacingbetween the trenches.

According to the seventh aspect of the invention, in a part of theparallel p-n layer laid out in the inactive region, the width of thesecond conductivity type semiconductor layer becomes larger than thewidth of the first conductivity type semiconductor layer. Therefore,interdiffusion of impurities between the first conductivity typesemiconductor layer and the second conductivity type semiconductor layermakes it possible to easily obtain a semiconductor device in which thetotal amount of impurities in the second conductivity type semiconductorlayer is larger than that in the first conductivity type semiconductorlayer.

A method of manufacturing a semiconductor device according to a eighthaspect of the invention is a method in which, in the method according tothe seventh aspect of the invention, in the step of forming the trenchesin the first conductivity type semiconductor layer, in a part of theregion to become the inactive region, trenches having widths larger thanthose of the trenches formed in the region to become the active regionare formed.

According to the eighth aspect of the invention, the aspect ratio of thetrench formed in a part of the region to become the inactive region canbe made lower than the aspect ratio of the trench in the region tobecome the active region. Therefore, the formation of the trench and thefilling the trench with an epitaxially grown semiconductor layer can beeasily carried out.

A method of manufacturing a semiconductor device according to a ninthaspect of the invention is a method which, in the method according toany one of the sixth aspect to the eighth aspect of the invention,further includes the step of removing a part of each of the secondconductivity type semiconductor layers filling the trenches by an amountgrown to a level higher than the surface of the insulator film used as amask for forming the trench by polishing the part with the insulatorfilm further used as a polishing stopper, the step being carried outbetween the step of carrying out epitaxial growth of the secondconductivity type semiconductor layer to fill each of the trenches andthe step of polishing the parallel p-n layer to planarize the surfacethereof.

According to the ninth aspect of the invention, there can be eliminatedvariation in thicknesses of over-epitaxial parts of the secondconductivity type semiconductor layers grown higher than the insulatorlayer when epitaxial growth of the second conductivity typesemiconductor layer is carried out. Therefore, even though the width ofthe trench in the active region differ from that in the inactive region,the parallel p-n layer can be formed with a uniform depth. Themanufacturing method can be also applied to the case in which the widthof the trench in the active region is equal to that in the inactiveregion. In this case, the parallel p-n layer can be prevented from beingformed with non-uniform depth due to variation in the epitaxial process.

A method of manufacturing a semiconductor device according to a tenthaspect of the invention is the method which, when manufacturing asemiconductor device in which a parallel p-n layer with firstconductivity type semiconductor layers and second conductivity typesemiconductor layers being alternately joined is provided on a firstconductivity type low resistance semiconductor layer and the parallelp-n layer is laid out both in an active region in which a current flowsin a turned-on state and in an inactive region around the active region,includes the steps of: carrying out epitaxial growth of a firstconductivity type semiconductor layer on the first conductivity type lowresistance semiconductor layer; depositing an insulator film on thesurface of the epitaxially grown first conductivity type semiconductorlayer; carrying out patterning of the insulator film to form a mask forforming trenches; by using the patterned insulator film as a mask,forming a plurality of trenches in a region to become an active regionin the first conductivity type semiconductor layer and along with this,forming a plurality of trenches in a part of a region to become aninactive region in the first conductivity type semiconductor layer, thetrenches being formed with a spacing different from that of the trenchesformed in the region to become the active region; carrying out epitaxialgrowth of a second conductivity type semiconductor layer in each of thetrenches formed in the first conductivity type semiconductor layer tofill trenches with the second conductivity type semiconductor layers toa level equal to or higher than the level of the surface of theinsulator film used as the mask for forming the trenches; and polishingthe parallel p-n layer comprising the first conductivity typesemiconductor layers and the second conductivity type semiconductorlayers filling the trenches to planarize the surface of the parallel p-nlayer.

According to the tenth aspect of the invention, in a part of theparallel p-n layer laid out in the inactive region, there can be formedsecond conductivity type semiconductor layers arranged at spacingdifferent from that of the second conductivity type semiconductor layersin the parallel p-n layer laid out in the active region. Therefore, thetotal amount of impurities in the second conductivity type semiconductorlayer in the parallel p-n layer in the inactive region is made increasedto be larger than the total amount of impurities in the firstconductivity type semiconductor layer. This enhances depletion in theinactive region to reduce the electric field strength in the inactiveregion, by which a semiconductor device can be obtained which is capableof ensuring a sufficiently high breakdown voltage.

According to the invention, a semiconductor device provided with asuper-junction structure can be obtained which can ensure a sufficientlyhigh breakdown voltage. Moreover, a semiconductor device provided with asuper-junction structure can be obtained which is suited for beingmanufactured by the trench filling method. Furthermore, thesemiconductor device provided with the super-junction structure can bemanufactured by the trench filling method.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in greater detail with reference tocertain preferred embodiments thereof and the accompanying drawings,wherein:

FIG. 1 is a partial plan view showing a principal section of a verticalMOSFET chip as a semiconductor device according to an embodiment 1 ofthe invention;

FIG. 2 is a vertical cross sectional view showing a cross sectionalstructure taken on the cutting line A-A in FIG. 1;

FIG. 3 is a diagram showing impurity concentration distributions in thedepth direction in p-semiconductor layers of the semiconductor deviceaccording to the embodiment 1;

FIG. 4 is a diagram showing impurity concentration distributions in thedepth direction in n-semiconductor layers of the semiconductor deviceaccording to the embodiment 1;

FIG. 5 is a diagram showing relations among total amounts of impuritiesin the p-semiconductor layers and the n-semiconductor layers in aparallel p-n layer in the semiconductor device according to theembodiment 1;

FIG. 6 is a diagram showing impurity concentration distributions in thedepth direction in p-semiconductor layers of the semiconductor deviceaccording to the embodiment 2;

FIG. 7 is a diagram showing impurity concentration distributions in thedepth direction in n-semiconductor layers of the semiconductor deviceaccording to the embodiment 2;

FIG. 8 is a partial plan view showing a principal section of a verticalMOSFET chip as a semiconductor device according to an embodiment 3 ofthe invention;

FIG. 9 is a vertical cross sectional view showing a cross sectionalstructure taken on the cutting line B-B in FIG. 8;

FIG. 10 is a diagram showing impurity concentration distributions in thedepth direction in p-semiconductor layers of the semiconductor deviceaccording to the embodiment 5;

FIG. 11 is a diagram showing impurity concentration distributions in thedepth direction in n-semiconductor layers of the semiconductor deviceaccording to the embodiment 5;

FIG. 12 is a diagram showing relations among total amounts of impuritiesin the p-semiconductor layers and the n-semiconductor layers in aparallel p-n layer in the semiconductor device according to theembodiment 5;

FIG. 13 is a diagram showing impurity concentration distributions in thedepth direction in p-semiconductor layers of the semiconductor deviceaccording to the embodiment 6;

FIG. 14 is a diagram showing impurity concentration distributions in thedepth direction in n-semiconductor layers of the semiconductor deviceaccording to the embodiment 6;

FIG. 15 is a partial plan view showing a principal section of a verticalMOSFET chip as a semiconductor device according to an embodiment 9 ofthe invention;

FIG. 16 is a vertical cross sectional view showing a cross sectionalstructure taken on the cutting line C-C in FIG. 15;

FIG. 17 is a diagram showing relations among total amounts of impuritiesin p-semiconductor layers and n-semiconductor layers in a parallel p-nlayer in the semiconductor device according to the embodiment 10;

FIG. 18 is a partial plan view showing a principal section of a verticalMOSFET chip as a semiconductor device according to an embodiment 11 ofthe invention;

FIG. 19 is a vertical cross sectional view showing a cross sectionalstructure taken on the cutting line D-D in FIG. 18;

FIG. 20 is a diagram showing relations among total amounts of impuritiesin p-semiconductor layers and n-semiconductor layers in a parallel p-nlayer in the semiconductor device according to the embodiment 14;

FIG. 21 is a partial plan view showing a principal section of a verticalMOSFET chip as a semiconductor device according to an embodiment 17 ofthe invention;

FIG. 22 is a vertical cross sectional view showing a cross sectionalstructure taken on the cutting line E-E in FIG. 21;

FIG. 23 is a diagram schematically showing relations among widths ofp-semiconductor layers and n-semiconductor layers in a parallel p-nlayer in the semiconductor device according to the embodiment 17;

FIG. 24 is a diagram showing impurity concentration distributions in thedepth direction in p-semiconductor layers of the semiconductor deviceaccording to the embodiment 17;

FIG. 25 is a diagram showing impurity concentration distributions in thedepth direction in n-semiconductor layers of the semiconductor deviceaccording to the embodiment 17;

FIG. 26 is a diagram showing relations among total amounts of impuritiesin the p-semiconductor layers and the n-semiconductor layers in aparallel p-n layer in the semiconductor device according to theembodiment 17;

FIG. 27 is a diagram showing impurity concentration distributions in thedepth direction in p-semiconductor layers of a semiconductor deviceaccording to the embodiment 18;

FIG. 28 is a diagram showing impurity concentration distributions in thedepth direction in n-semiconductor layers of the semiconductor deviceaccording to the embodiment 18;

FIG. 29 is a partial plan view showing a principal section of a verticalMOSFET chip as a semiconductor device according to an embodiment 19 ofthe invention;

FIG. 30 is a vertical cross sectional view showing a cross sectionalstructure taken on the cutting line F-F in FIG. 29;

FIG. 31 is a diagram showing impurity concentration distributions in thedepth direction in p-semiconductor layers of a semiconductor deviceaccording to the embodiment 21;

FIG. 32 is a diagram showing impurity concentration distributions in thedepth direction in n-semiconductor layers of the semiconductor deviceaccording to the embodiment 21;

FIG. 33 is a diagram showing relations among total amounts of impuritiesin the p-semiconductor layers and the n-semiconductor layers in aparallel p-n layer in the semiconductor device according to theembodiment 21;

FIG. 34 is a diagram showing impurity concentration distributions in thedepth direction in p-semiconductor layers of a semiconductor deviceaccording to the embodiment 22;

FIG. 35 is a diagram showing impurity concentration distributions in thedepth direction in n-semiconductor layers of the semiconductor deviceaccording to the embodiment 22;

FIG. 36 is a vertical cross sectional view showing a structure of asemiconductor device in the course of being manufactured by a methodaccording to an embodiment 25 of the invention with an n-epitaxial layerbeing formed on a n-semiconductor substrate;

FIG. 37 is a vertical cross sectional view showing the structure of thesemiconductor device in the course of being manufactured by the methodaccording to the embodiment 25 with trenches being formed in then-epitaxial layer;

FIG. 38 is a vertical cross sectional view showing the structure of thesemiconductor device in the course of being manufactured by the methodaccording to the embodiment 25 with the trenches being filled withp-epitaxial layers;

FIG. 39 is a vertical cross sectional view showing the structure of thesemiconductor device in the course of being manufactured by the methodaccording to the embodiment 25 with portions of the p-epitaxial layersgrown above the surfaces of oxide films being removed by polishing;

FIG. 40 is a vertical cross sectional view showing the structure of thesemiconductor device in the course of being manufactured by the methodaccording to the embodiment 25 with the oxide films being removed;

FIG. 41 is a vertical cross sectional view showing the structure of thesemiconductor device in the course of being manufactured by the methodaccording to the embodiment 25 with both of the surfaces of the n- andp-epitaxial layers being polished to be provided as a super-junctionsemiconductor substrate;

FIG. 42 is a vertical cross sectional view showing a structure of asemiconductor device in the course of being manufactured by a methodaccording to an embodiment 26 of the invention with trenches beingformed in the n-epitaxial layer;

FIG. 43 is a vertical cross sectional view showing the structure of thesemiconductor device in the course of being manufactured by the methodaccording to the embodiment 26 with the trenches being filled withp-epitaxial layers;

FIG. 44 is a vertical cross sectional view showing the structure of thesemiconductor device in the course of being manufactured by the methodaccording to the embodiment 26 with portions of the p-epitaxial layersgrown above the surfaces of oxide films being removed by polishing;

FIG. 45 is a vertical cross sectional view showing the structure of thesemiconductor device in the course of being manufactured by the methodaccording to the embodiment 26 with the oxide films being removed;

FIG. 46 is a vertical cross sectional view showing the structure of thesemiconductor device in the course of being manufactured by the methodaccording to the embodiment 26 with both of the surfaces of the n- andp-epitaxial layers being polished to be provided as a super-junctionsemiconductor substrate; and

FIG. 47 is a diagram showing relations among total amounts of impuritiesin the p-semiconductor layers and the n-semiconductor layers in aparallel p-n layer in a related semiconductor device.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In the following, preferred embodiments of the invention will beexplained in detail with reference to the attached drawings. In thefollowing explanations and the attached drawings, a leading character“n” or “p” attached to names of layers and regions means that carriersin the layers and the regions are electrons or holes, respectively.Moreover, a sign “+” or “++” attached to the right and above of theleading character “n” or “p” represents that impurity concentration inthe layer or the region is comparatively high, or further higher,respectively.

Furthermore, in all of the drawings, similar arrangements are denotedwith the same reference numerals and signs with redundant explanationsbeing omitted. Moreover, in the following explanations, a section alonga side extending in the direction perpendicular to the stripes of theparallel p-n layer is to be simply expressed as “a section perpendicularto the stripes”. Furthermore, a section along a side extending in thedirection parallel to the stripes of the parallel p-n layer is to besimply expressed as “a section parallel to the stripes”.

FIG. 1 is a partial plan view showing a principal section of a verticalMOSFET chip according to a first embodiment of the invention. In FIG. 1,illustrations of the surface layer of the parallel p-n layer and surfacestructures of elements formed thereon are omitted. As shown in FIG. 1,an active region 100, in which a current flows in the turned-on state ofthe MOSFET, is located in the central section of the chip formed in arectangular shape, for example. The region 100 is further surroundedwith an inactive region 200 provided in the peripheral section of thechip. The parallel p-n layer is formed to have a stripe-pattern-likeplane figure in which n-semiconductor layers 2 a and p-semiconductorlayers 2 b are alternately joined, and further n-semiconductor layers 3a and p-semiconductor layers 3 b are alternately joined. The end sectionof the chip is provided as an n-semiconductor layer 13.

Here, for differentiating between the n-semiconductor layer 2 a and then-semiconductor layer 3 a forming the parallel p-n layer, they arereferred to as a first n-semiconductor layer 2 a and a secondn-semiconductor layer 3 a, respectively. About the p-semiconductor layer2 b and the p-semiconductor layer 3 b, they are similarly referred to asa first p-semiconductor layer 2 b and a second p-semiconductor layer 3b, respectively. Moreover, the parallel p-n layer including the firstn-semiconductor layer 2 a and the first p-semiconductor layer 2 b isreferred to as a first parallel p-n layer. Similarly, the parallel p-nlayer including the second n-semiconductor layer 3 a and the secondp-semiconductor layer 3 b is referred to as a second parallel p-n layer.

The width of and the total amount of the impurity concentration in thefirst n-semiconductor layer 2 a are approximately equal to the width ofand the total amount of the impurity concentration in the firstp-semiconductor layer 2 b. The width of the second p-semiconductor layer3 b is larger than those of the second n-semiconductor layer and thefirst p-semiconductor layer 2 b. The total amount of the impurities inthe second p-semiconductor layer 3 b is larger than that of the secondn-semiconductor layer 3 a. Moreover, The width of each of the firstn-semiconductor layer 2 a, the first p-semiconductor layer 2 b, thesecond n-semiconductor layer 3 a and the second p-semiconductor layer 3b is unchanged through its extending direction parallel to the stripesof the parallel p-n layer.

In the first embodiment, the parallel p-n layer in the active region 100is made up of the first parallel p-n layer. Therefore, in the activeregion 100, charges are balanced. Moreover, in the inactive region 200,the parallel p-n layer in the section parallel to the stripes is made upof the first parallel p-n layer and the second parallel p-n layer.Therefore, in a part of the section parallel to the stripes in theinactive region 200, charges are brought into an unbalanced state. Inthe inactive region 200, the parallel p-n layer in the sectionperpendicular to the stripes is made up of the first parallel p-n layercontinuously provided from the active region 100. When the MOSFET is ina turned-off state, the parallel p-n layer in the section perpendicularto the stripes in the inactive section 200 is operated as the lateralsuper-junction structure, which can sufficiently ensure a sufficientlyhigh breakdown voltage.

FIG. 2 is a vertical cross sectional view showing a cross sectionalstructure taken on the cutting line A-A traversing the active region andthe inactive region in FIG. 1 in the direction perpendicular to thestripes. In FIG. 2, the right-hand section is the active region 100driving a current as the MOSFET and the left-hand section is theinactive region 200 forming a peripheral voltage withstanding structureon the outside of the active region 100. Over the active region 100 andthe inactive region 200, an n⁺⁺-drain layer 1 is provided. Then-semiconductor layers 2 a and 3 a, and the p-semiconductor layers 2 band 3 b are provided on the surface of the n⁺⁺-drain layer 1.

On the element top surface side in the active region 100 and on theelement top surface side of a portion near the boundary of the inactiveregion 200 with the active region 100, there is formed an elementsurface structure with n-channel MOSFETs. Each n-channel MOSFET includesa p-base region 4, a p⁺-contact region 5, an n⁺-source region 6, a gateinsulator film 7, a gate electrode 8, an interlayer insulator film 9 aof, for example, an oxide film, and a source electrode 10. On the bottomsurface of the n⁺⁺-drain layer 1, a drain electrode 11 is provided.

The top surface of the inactive region 200 is coated with an interlayerinsulator film 9 b except for the portion near the boundary with theactive region 100 and a chip end section. The source electrode 10extends from the active region 100 to the inactive region 200 to coverhalfway the interlayer insulator layer 9 b covering the inactive region200. While, at the end of the chip, a stopper electrode 12 is provided.The stopper electrode 12 is in contact with an n⁺-semiconductor region14 provided on the top surface layer of the n-semiconductor layer 13 inthe chip end section and covers the chip end side portion of theinterlayer insulator film 9 b covering the inactive region 200.

As shown in FIG. 2, in the first embodiment, in the inactive region 200,the first parallel p-n layer is laid out in a region ranging from theboundary with the active region 100 to the section under the portion ofthe source electrode 10 close to its end. Furthermore, the secondparallel p-n layer is laid out in a region ranging from the sectionunder the portion of the source electrode 10 close to its end to then-semiconductor layer 13. In other words, in the inactive region 200,the position of the boundary between the first parallel p-n layer andthe second parallel p-n layer is at the thickest possible portion of theinterlayer insulator film 9 b covering the inactive region. Thereference to the “thickest portion” of the interlayer insulator film 9 brefers to the fact that the interlayer insulating film 9 a is formed inan active region and is not as thick as the interlayer insulating film 9b. Moreover, the boundary is also positioned under the source electrode10 extending over the interlayer insulator film 9 b. This is forreducing electric field strength. The electric field strength, becomingthe strongest on the outside of the source electrode 10, is reduced bylaying out p-regions with total amounts of impurities increased to belarger than those in n-regions in the section where the electric fieldstrength becomes the strongest to enhance depletion in the n-regions.

Next, explanations will be made about relations in impurityconcentration distributions and in total amounts of impurities in thefirst parallel p-n layer and the second parallel p-n layer. Forconvenience of explanations, as shown in FIG. 2, in the first parallelp-n layer, the impurity concentration in the first n-semiconductor layer2 a is referred to as an1 both in the proximity of the boundary with thegate insulator film 7 in the active region 100 and in the proximity ofthe boundary with the interlayer insulator film 9 b in the inactiveregion 200. In the proximity of the boundary with the n⁺⁺-drain layer 1,the impurity concentration in the first n-semiconductor layer 2 a isfurther referred to as an2 both in the active region 100 and in theinactive region 200.

Moreover, in the first parallel p-n layer, the impurity concentration inthe first p-semiconductor layer 2 b is referred to as ap1 both in theproximity of the boundary with the source electrode 10 in the activeregion 100 and in the proximity of the boundary with the interlayerinsulator film 9 b in the inactive region 200. In the proximity of theboundary with the n⁺⁺-drain layer 1, the impurity concentration in thefirst p-semiconductor layer 2 b is further referred to as ap2 both inthe active region 100 and in the inactive region 200. In the same way,in the second parallel p-n layer, the impurity concentrations in thesecond n-semiconductor layer 3 a and the second p-semiconductor layer 3b are referred to as en1 and ep1, respectively, in the proximity of theboundary with the interlayer insulator film 9 b. In the proximity of theboundary with the n⁺⁺-drain layer 1, the impurity concentrations in thesecond n-semiconductor layer 3 a and the second p-semiconductor layer 3b are referred to as en2 and ep2, respectively.

FIG. 3 is a diagram showing impurity concentration distributions in thedepth direction in the p-semiconductor layers of the semiconductordevice according to the embodiment 1. As shown in FIG. 3, both of theimpurity concentration distribution in the depth direction in the firstp-semiconductor layer 2 b, denoted by numeral 41, and the impurityconcentration distribution in the depth direction in the secondp-semiconductor layer 3 b, denoted by numeral 42, are uniform. Moreover,the value Np1 of the impurity concentration in the secondp-semiconductor layer 3 b is higher than the value Np0 of the impurityconcentration in the first p-semiconductor layer 2 b. Furthermore, FIG.4 is a diagram showing impurity concentration distributions in the depthdirection in the n-semiconductor layers of the semiconductor deviceaccording to the embodiment 1. As shown in FIG. 4, the impurityconcentration distribution in the depth direction in the firstn-semiconductor layer 2 a, denoted by numeral 43, and the impurityconcentration distribution in the depth direction in the secondn-semiconductor layer 3 a, denoted by numeral 44, are uniform. Inaddition, the value Nn1 of the impurity concentration in the secondn-semiconductor layer 3 a is lower than the value Nn0 of the impurityconcentration in the first n-semiconductor layer 2 a. The value Np0 ofthe impurity concentration in the first p-semiconductor layer 2 b isapproximately equal to the value Nn0 of the impurity concentration inthe first n-semiconductor layer 2 a, though the conductivity types ofthe impurities are different from each other.

Such impurity concentration distributions, as will be explained in thelater given description of the embodiment 25, can be achieved byinterdiffusion of impurities between the n-semiconductor layer and thep-semiconductor layer. The interdiffusion occurs when the elementsurface structures of the MOSFETs are formed via the high temperatureprocess carried out after making epitaxial growth of the p-semiconductorlayers in the trenches formed in the n-semiconductor layer. Theinterdiffusion of impurities causes the impurity concentrations in thep-semiconductor layer and the n-semiconductor layer to depend on thewidths of the respective layers.

Here, the width of the first p-semiconductor layer 2 b and the width ofthe first n-semiconductor layer 2 a are approximately equal to eachother. While, as explained above, the width of the secondp-semiconductor layer 3 b is larger than the width of the secondn-semiconductor layer 3 a. Therefore, relations among total amounts ofimpurities in the first n-semiconductor layer 2 a, the firstp-semiconductor layer 2 b, the second n-semiconductor layer 3 a and thesecond p-semiconductor layer 3 b are as shown in FIG. 5. However, FIG. 5only illustrates relations of large or small among total amounts ofimpurities in the semiconductor layers. Thus, the figure does notillustrate so far as how large or how small the total amounts ofimpurities are among them.

Namely, the total amount of impurities in the first p-semiconductorlayer 2 b, denoted by numeral 45, is approximately equal to the totalamount of impurities in the first n-semiconductor layer 2 a, denoted bynumeral 47. Moreover, the total amount of impurities in the secondp-semiconductor layer 3 b, denoted by numeral 46, becomes larger thanthe total amount of impurities 45 in the first p-semiconductor layer 2 band the total amount of impurities 47 in the first n-semiconductor layer2 a. While, the total amount of impurities in the second n-semiconductorlayer 3 a, denoted by numeral 48, becomes smaller than the total amountof impurities 45 in the first p-semiconductor layer 2 b and the totalamount of impurities 47 in the first n-semiconductor layer 2 a.

Although the invention is not particularly limited to the following,there will be shown dimensions of and impurity concentrations in somemain parts as examples. The impurity concentration in the n⁺⁺-drainlayer 1 is on the order of 2×10¹⁸ cm⁻³. In the first parallel p-n layer,the width of the first p-semiconductor layer 2 b and the width of thefirst n-semiconductor layer 2 a are both about 5 μm. The impurityconcentration in the first p-semiconductor layer 2 b and the impurityconcentration in the first n-semiconductor layer 2 a are both on theorder of 4.5×10¹⁵ cm⁻³.

In the second parallel p-n layer, the width of the secondp-semiconductor layer 3 b and the width of the second n-semiconductorlayer 3 a are about 6 μm and about 4 μm, respectively. The impurityconcentration in the second p-semiconductor layer 3 b and the impurityconcentration in the second n-semiconductor layer 3 a are on the orderof 5.5×10¹⁵ cm⁻³ and on the order of 3.0×10¹⁵ cm⁻³, respectively. Theeffective length of the parallel p-n layer in the depth direction isabout 45 μm.

As explained above, since the charges in the parallel p-n layer laid outin the voltage withstanding structure section in the inactive region 200are in an unbalanced state, it is considered that the breakdown voltageof the section directly below the source electrode 10 is lowered.However, the interlayer insulator film 9 b provided directly below thesource electrode 10 withstands the voltage equivalent to the loweredportion of the breakdown voltage to cause no lowering in the breakdownvoltage in total. Moreover, on the outside of the end of the sourceelectrode 10, the second n-semiconductor layer 3 a in the secondparallel p-n layer, having the width being narrow and the impurityconcentration being lowered, causes a depletion layer easy to expandoutward. Therefore, a sufficiently high breakdown voltage can beensured.

The second embodiment is a vertical MOSFET chip in which, in thevertical MOSFET chip of the first embodiment, the impurityconcentrations in the second p-semiconductor layer 3 b and the secondn-semiconductor layer 3 a in the second parallel p-n layer are madeapproximately equal to those in the first p-semiconductor layer 2 b andthe first n-semiconductor layer 2 a in the first parallel p-n layer. Theplane structure of the parallel p-n layer is the same as that shown inFIG. 1. Moreover, the cross sectional structure taken on the cuttingline A-A in FIG. 1 is the same as that shown in FIG. 2. Dimensions,impurity concentrations and the like in all parts are, unless otherwisenotified, the same as those in the embodiment 1.

FIG. 6 is a diagram showing impurity concentration distributions in thedepth direction in the p-semiconductor layers of the semiconductordevice according to the embodiment 2. As shown in FIG. 6, both of theimpurity concentration distribution in the depth direction in the firstp-semiconductor layer 2 b, denoted by numeral 51, and the impurityconcentration distribution in the depth direction in the secondp-semiconductor layer 3 b, denoted by numeral 52, are uniform withimpurity concentration values approximately equal to each other, eachvalue being approximately equal to Np0. Moreover, FIG. 7 is a diagramshowing impurity concentration distributions in the depth direction inthe n-semiconductor layers of the semiconductor device according to theembodiment 2. As shown in FIG. 7, both of the impurity concentrationdistribution in the depth direction in the first n-semiconductor layer 2a, denoted by numeral 53, and the impurity concentration distribution inthe depth direction in the second n-semiconductor layer 3 a, denoted bynumeral 54, are uniform with impurity concentration values approximatelyequal to each other, each value being approximately equal to Nn0.Furthermore, the value Np0 of the impurity concentration in each of thefirst p-semiconductor layer 2 b and the second p-semiconductor layer 3 bis approximately equal to the value Nn0 of the impurity concentration ineach of the first n-semiconductor layer 2 a and the secondn-semiconductor layer 3 a, though the conductivity types of theimpurities are different from each other. For example, all of the firstp-semiconductor layer 2 b, the first n-semiconductor layer 2 a, thesecond p-semiconductor layer 3 b and the second n-semiconductor layer 3a have an impurity concentration of the order of 4.5×10¹⁵ cm⁻³.

Such impurity concentration distributions, as will be explained in thelater given description of the embodiment 27, can be achieved by formingthe element surface structures of the MOSFET under a low temperatureprocess so as not to cause interdiffusion of impurities between then-semiconductor layer and the p-semiconductor layer. The low temperatureprocess is carried out after forming the p-semiconductor layers byepitaxial growth in the trenches formed in the n-semiconductor layer.This makes the impurity concentrations in the n-semiconductor layers andthe p-semiconductor layers in the parallel p-n layer approximately equalto those of the substrate and the epitaxial layers filling the trenches,respectively, even though the widths of the p-semiconductor layers andthe n-semiconductor layers in the parallel p-n layer differ from oneanother.

The width of the first p-semiconductor layer 2 b and that of the firstn-semiconductor layer 2 a are approximately equal to each other. Thus,the total amount of impurities in the first p-semiconductor layer 2 band that in the first n-semiconductor layer 2 a become approximatelyequal to each other. While, the width of the second p-semiconductorlayer 3 b is larger than that of the first p-semiconductor layer 2 b.Thus, the total amount of impurities in the second p-semiconductor layer3 b becomes larger than that in the first p-semiconductor layer 2 b.Moreover, the width of the second n-semiconductor layer 3 a is smallerthan that of the first n-semiconductor layer 2 a. Thus, the total amountof impurities in the second n-semiconductor layer 3 a becomes smallerthan that in the first n-semiconductor layer 2 a. Therefore, therelations of being large or small among total amounts of impurities inthe first n-semiconductor layer 2 a, the first p-semiconductor layer 2b, the second n-semiconductor layer 3 a and the second p-semiconductorlayer 3 b in the embodiment 2, when illustrated without taking thedegree of being large or small into consideration, become as shown inFIG. 5.

As explained above, in the embodiment 2, by forming the element surfacestructures of the MOSFET by a low temperature process, no interdiffusionof impurities due to heat history occurs to facilitate the control ofthe impurity concentrations in the parallel p-n layer. This thereforeenables almost direct realization of a structure determined byperforming numerical calculations such as computer simulations.

FIG. 8 is a partial plan view showing a principal section of a verticalMOSFET chip according to an embodiment 3 of the invention. In FIG. 8,illustrations of the surface layer of the parallel p-n layer and surfacestructures of elements formed thereon are omitted. FIG. 9 is a verticalcross sectional view showing a cross sectional structure taken on thecutting line B-B traversing the active region and the inactive region inFIG. 8 in the direction perpendicular to the stripes.

As shown in FIG. 8 and FIG. 9, the third embodiment is a vertical MOSFETchip in which, in the inactive region 210, the whole parallel p-n layerin the section parallel to the stripes is made up of the second parallelp-n layer with charges being in an unbalanced state. Therefore, in aportion of the inactive region 210 in the proximity of the boundary withthe active region 100, the second parallel p-n layer is laid out also ina portion where the source electrode 10 is in contact with thesemiconductor surface, that is, in a portion without the interlayerinsulator film 9 b. The arrangements other than the above, dimensions,impurity concentrations and the like in all parts are the same as thosein the embodiment 1.

In the above-explained arrangement, the breakdown voltage in the depthdirection is lowered in the second parallel p-n layer with unbalancedcharges. Thus, an avalanche occurs at a portion at which the sourceelectrode 10 is in contact with the semiconductor surface in theinactive region 210. Therefore, compared with the case in whichavalanche breakdown occurs below the interlayer insulator film 9 b, anavalanche current is efficiently pulled out from the source electrode 10to cause no concentration of current, which enhances avalanchedurability.

The fourth embodiment is a vertical MOSFET chip in which, in thevertical MOSFET chip of the third embodiment, the impurityconcentrations in the second p-semiconductor layer 3 b and the secondn-semiconductor layer 3 a in the second parallel p-n layer are madeapproximately equal to those in the first p-semiconductor layer 2 b andthe first n-semiconductor layer 2 a in the first parallel p-n layer. Theplane structure of the parallel p-n layer is the same as that shown inFIG. 8. Moreover, the cross sectional structure taken on the cuttingline B-B in FIG. 8 is the same as that shown in FIG. 9. Dimensions,impurity concentrations and the like in all parts are, unless otherwisenotified, the same as those in the embodiment 3.

The distribution in the depth direction of each of the impurityconcentrations in the first p-semiconductor layer 2 b and the secondp-semiconductor layer 3 b is as shown in FIG. 6. Moreover, thedistribution in the depth direction of each of the impurityconcentrations in the first n-semiconductor layer 2 a and the secondn-semiconductor layer 3 a is as shown in FIG. 7. Furthermore, the valueNp0 of the impurity concentration in each of the first p-semiconductorlayer 2 b and the second p-semiconductor layer 3 b is approximatelyequal to the value Nn0 of the impurity concentration in each of thefirst n-semiconductor layer 2 a and the second n-semiconductor layer 3a, though the conductivity types of the impurities are different fromeach other.

For example, all of the first p-semiconductor layer 2 b, the firstn-semiconductor layer 2 a, the second p-semiconductor layer 3 b and thesecond n-semiconductor layer 3 a have an impurity concentration of theorder of 4.5×10¹⁵ cm⁻³. As explained about the embodiment 2, therelations of being large or small among total amounts of impurities inthe first n-semiconductor layer 2 a, the first p-semiconductor layer 2b, the second n-semiconductor layer 3 a and the second p-semiconductorlayer 3 b in the fourth embodiment, when illustrated without taking thedegree of being large or small into consideration, become as shown inFIG. 5.

Embodiment 5

The fifth embodiment is a vertical MOSFET chip in which, the impurityconcentration in the first p-semiconductor layer 2 b in the firstparallel p-n layer and the impurity concentration in the secondp-semiconductor layer 3 b in the second parallel p-n layer are madehigher than those in the embodiment 1 to make the charges in the firstparallel p-n layer in an unbalanced state also in the active region 100.The plane structure of the parallel p-n layer is the same as that shownin FIG. 1. Moreover, the cross sectional structure taken on the cuttingline A-A in FIG. 1 is the same as that shown in FIG. 2. Dimensions,impurity concentrations and the like in all parts are, unless otherwisenotified, the same as those in the embodiment 1.

FIG. 10 is a diagram showing impurity concentration distributions in thedepth direction in the p-semiconductor layers of the semiconductordevice according to the embodiment 5. As shown in FIG. 10, both of theimpurity concentration distribution in the depth direction in the firstp-semiconductor layer 2 b, denoted by numeral 61, and the impurityconcentration distribution in the depth direction in the secondp-semiconductor layer 3 b, denoted by numeral 62, are uniform. Moreover,the value Np1 of the impurity concentration in the secondp-semiconductor layer 3 b is higher than the value Np0 of the impurityconcentration in the first p-semiconductor layer 2 b. Furthermore, FIG.11 is a diagram showing impurity concentration distributions in thedepth direction in the n-semiconductor layers of the semiconductordevice according to the embodiment 5. As shown in FIG. 11, the impurityconcentration distribution in the depth direction in the firstn-semiconductor layer 2 a, denoted by numeral 63, and the impurityconcentration distribution in the depth direction in the secondn-semiconductor layer 3 a, denoted by numeral 64, are uniform. Inaddition, the value Nn1 of the impurity concentration in the secondn-semiconductor layer 3 a is lower than the value Nn0 of the impurityconcentration in the first n-semiconductor layer 2 a. The value Np0 ofthe impurity concentration in the first p-semiconductor layer 2 b ishigher than the value Nn0 of the impurity concentration in the firstn-semiconductor layer 2 a, though the conductivity types of theimpurities are different from each other.

For example, the impurity concentrations in the first p-semiconductorlayer 2 b is on the order of 4.7×10¹⁵ cm⁻³, and the impurityconcentration in the first n-semiconductor layer 2 a is on the order of4.5×10¹⁵ cm⁻³. The impurity concentration in the second p-semiconductorlayer 3 b is on the order of 5.8×10¹⁵ cm⁻³, and the impurityconcentration in the second n-semiconductor layer 3 a is on the order of3.0×10¹⁵ cm⁻³.

In the first p-semiconductor layer 2 b and the first n-semiconductorlayer 2 a, their widths are approximately equal to each other, while theimpurity concentrations in them differ from each other. Thus, as shownin FIG. 12 illustrating relations among total amounts of impurities inthe p-semiconductor layers and the n-semiconductor layers in theparallel p-n layer, the total amount of impurities in the firstp-semiconductor layer 2 b, denoted by numeral 65, becomes larger thanthe total amount of impurities in the first n-semiconductor layer 2 a,denoted by numeral 67. Moreover, the width of the second p-semiconductorlayer 3 b is larger than the width of the first p-semiconductor layer 2b. Thus, the total amount of impurities in the second p-semiconductorlayer 3 b, denoted by numeral 66, becomes larger than the total amountof impurities 65 in the first p-semiconductor layer 2 b.

Furthermore, the width of the second n-semiconductor layer 3 a issmaller than the width of the first n-semiconductor layer 2 a. Thus, thetotal amount of impurities in the second n-semiconductor layer 3 a,denoted by numeral 68, becomes smaller than the total amount ofimpurities 67 in the first n-semiconductor layer 2 a. However, FIG. 12only illustrates relations of large or small among total amounts ofimpurities in the semiconductor layers. Thus, the figure does notillustrate so far as how large or how small the total amounts ofimpurities are among them.

In the above-explained arrangement, in the inactive region 200, theimpurity concentration in the second p-semiconductor layer 3 b is higherthan that in the embodiment 1 and the total amount of impurities in thesecond p-semiconductor layer 3 b is larger than that in theembodiment 1. Thus, a depletion layer is made to expand in the inactiveregion 200 more easily than in the embodiment 1. This increases abreakdown voltage in the inactive region 200 to become higher than thebreakdown voltage in the active region 100. Therefore, avalanchebreakdown occurs in the active region 100, which makes concentration ofan avalanche current hard to occur to enhance avalanche durability.Moreover, the impurity concentration made higher in the firstp-semiconductor layer 2 b in the active region 100 suppresses negativeresistance component even though a hole current is accumulated when anavalanche current is generated. This further enhances avalanchedurability.

The sixth embodiment is a vertical MOSFET chip in which, in the verticalMOSFET chip of the third embodiment, the impurity concentrations in thesecond p-semiconductor layer 3 b and the second n-semiconductor layer 3a in the second parallel p-n layer are made approximately equal to thosein the first p-semiconductor layer 2 b and the first n-semiconductorlayer 2 a in the first parallel p-n layer, respectively. The planestructure of the parallel p-n layer is the same as that shown in FIG. 1.Moreover, the cross sectional structure taken on the cutting line A-A inFIG. 1 is the same as that shown in FIG. 2. Dimensions, impurityconcentrations and the like in all parts are, unless otherwise notified,the same as those in the embodiment 5.

FIG. 13 is a diagram showing impurity concentration distributions in thedepth direction in the p-semiconductor layers of the semiconductordevice according to the embodiment 6. As shown in FIG. 13, both of theimpurity concentration distribution in the depth direction in the firstp-semiconductor layer 2 b, denoted by numeral 71, and the impurityconcentration distribution in the depth direction in the secondp-semiconductor layer 3 b, denoted by numeral 72, are uniform withimpurity concentration values approximately equal to each other, eachvalue being approximately equal to Np0. Moreover, FIG. 14 is a diagramshowing impurity concentration distributions in the depth direction inthe n-semiconductor layers of the semiconductor device according to theembodiment 6. As shown in FIG. 14, the impurity concentrationdistribution in the depth direction in the first n-semiconductor layer 2a, denoted by numeral 73, and the impurity concentration distribution inthe depth direction in the second n-semiconductor layer 3 a, denoted bynumeral 74, are uniform with impurity concentration values approximatelyequal to each other, each value being approximately equal to Nn0. Inaddition, the value Np0 of the impurity concentration in each of thefirst p-semiconductor layer 2 b and the second p-semiconductor layer 3 bis higher than the value Nn0 of the impurity concentration in each ofthe first n-semiconductor layer 2 a and the second n-semiconductor layer3 a, though the conductivity types of the impurities are different fromeach other.

For example, both of the first p-semiconductor layer 2 b and the secondp-semiconductor layer 3 b have an impurity concentration of the order of4.7×10¹⁵ cm⁻³. Both of the first n-semiconductor layer 2 a and thesecond n-semiconductor layer 3 a have an impurity concentration of theorder of 4.5×10¹⁵ cm⁻³.

In the first p-semiconductor layer 2 b and the first n-semiconductorlayer 2 a, their widths are approximately equal to each other, while theimpurity concentrations in them differ from each other. Thus, the totalamount of impurities in the first p-semiconductor layer 2 b becomeslarger than the total amount of impurities in the first n-semiconductorlayer 2 a. Moreover, the width of the second p-semiconductor layer 3 bis larger than the width of the first p-semiconductor layer 2 b. Thus,the total amount of impurities in the second p-semiconductor layer 3 bbecomes larger than the total amount of impurities in the firstp-semiconductor layer 2 b. While, the width of the secondn-semiconductor layer 3 a is smaller than the width of the firstn-semiconductor layer 2 a. Thus, the total amount of impurities in thesecond n-semiconductor layer 3 a becomes smaller than the total amountof impurities in the first n-semiconductor layer 2 a. Therefore, therelations of being large or small among total amounts of impurities inthe first n-semiconductor layer 2 a, the first p-semiconductor layer 2b, the second n-semiconductor layer 3 a and the second p-semiconductorlayer 3 b in the embodiment 6, when illustrated without taking thedegree of being large or small into consideration, become as shown inFIG. 12.

The seventh embodiment is a vertical MOSFET chip in which, in thevertical MOSFET chip of the embodiment 3, the whole parallel p-n layerin the section parallel to the stripes in the inactive region 210 ismade up of the second parallel p-n layer with charges being in anunbalanced state. The plane structure of the parallel p-n layer is thesame as that shown in FIG. 8. Moreover, the cross sectional structuretaken on the cutting line B-B in FIG. 8 is the same as that shown inFIG. 9. Dimensions, impurity concentrations and the like in all partsare, unless otherwise notified, the same as those in the thirdembodiment.

The eighth embodiment is a vertical MOSFET chip in which, in thevertical MOSFET chip of the embodiment 3, the whole parallel p-n layerin the section parallel to the stripes in the inactive region 210 ismade up of the second parallel p-n layer with charges being in anunbalanced state. Along with this, the impurity concentrations in thesecond p-semiconductor layer 3 b and the second n-semiconductor layer 3a in the second parallel p-n layer are made approximately equal to thosein the first p-semiconductor layer 2 b and the first n-semiconductorlayer 2 a in the first parallel p-n layer, respectively. The planestructure of the parallel p-n layer is the same as that shown in FIG. 8.Moreover, the cross sectional structure taken on the cutting line B-B inFIG. 8 is the same as that shown in FIG. 9. Dimensions, impurityconcentrations and the like in all parts are, unless otherwise notified,the same as those in the third embodiment.

The distribution in the depth direction of each of the impurityconcentrations in the first p-semiconductor layer 2 b and the secondp-semiconductor layer 3 b, denoted by numerals 71 and 72 respectively,is as shown in FIG. 13. Moreover, the distribution in the depthdirection of each of the impurity concentrations in the firstn-semiconductor layer 2 a and the second n-semiconductor layer 3 a,denoted by numerals 73 and 74 respectively, is as shown in FIG. 14. Inaddition, the value Np0 of the impurity concentration in each of thefirst p-semiconductor layer 2 b and the second p-semiconductor layer 3 bis higher than the value Nn0 of the impurity concentration in each ofthe first n-semiconductor layer 2 a and the second n-semiconductor layer3 a.

For example, both of the first p-semiconductor layer 2 b and the secondp-semiconductor layer 3 b have an impurity concentration of the order of4.7×10¹⁵ cm⁻³. Both of the first n-semiconductor layer 2 a and thesecond n-semiconductor layer 3 a have an impurity concentration of theorder of 4.5×10¹⁵ cm⁻³. Moreover, as was explained in the description ofthe sixth embodiment, the relations of being large or small among totalamounts of impurities in the first n-semiconductor layer 2 a, the firstp-semiconductor layer 2 b, the second n-semiconductor layer 3 a and thesecond p-semiconductor layer 3 b in the embodiment 8, when illustratedwithout taking the degree of being large or small into consideration,become as shown in FIG. 12.

FIG. 15 is a partial plan view showing a principal section of a verticalMOSFET chip according to an embodiment 9 of the invention. In FIG. 15,illustrations of the surface layer of the parallel p-n layer and surfacestructures of elements formed thereon are omitted. FIG. 16 is a verticalcross sectional view showing a cross sectional structure taken on thecutting line C-C traversing the active region and the inactive region inFIG. 15 in the direction perpendicular to the stripes.

As shown in FIG. 15 and FIG. 16, the ninth embodiment is a verticalMOSFET chip in which, in the second parallel p-n layer in the sectionparallel to the stripes in the inactive region 220, the width of thesecond p-semiconductor layer 3 b is made equal to that of the firstp-semiconductor layer 2 b. While, the width of the secondn-semiconductor layer 3 a is made smaller than the width of the firstn-semiconductor layer 2 a in the first parallel p-n layer. Therefore, inthe second parallel p-n layer, the state of interdiffusion of impuritiesbetween the second n-semiconductor layer 3 a and the secondp-semiconductor layer 3 b is made different from that in the firstembodiment. This makes impurity concentrations in both of the secondn-semiconductor layer 3 a and the second p-semiconductor layer 3 bdifferent from those in the embodiment 1. The arrangements other thanthe above, dimensions, impurity concentrations and the like in all partsare, unless otherwise notified, the same as those in the embodiment 1.

The distribution in the depth direction of each of the impurityconcentrations in the first p-semiconductor layer 2 b and the secondp-semiconductor layer 3 b is as shown in FIG. 3. Moreover, thedistribution in the depth direction of each of the impurityconcentrations in the first n-semiconductor layer 2 a and the secondn-semiconductor layer 3 a is as shown in FIG. 4. Furthermore, the valueNp0 of the impurity concentration in the first p-semiconductor layer 2 bis approximately equal to the value Nn0 of the impurity concentration inthe first n-semiconductor layer 2 a, though the conductivity types ofthe impurities are different from each other.

For example, the impurity concentrations in the second p-semiconductorlayer 3 b is on the order of 5.0×10¹⁵ cm⁻³, and the impurityconcentration in the second n-semiconductor layer 3 a is on the order of2.0×10¹⁵ cm⁻³. Moreover, the width of the second n-semiconductor layer 3a is about 3.5 μm, and the width of the second p-semiconductor layer 3 bis about 5.0 μm. The relations of being large or small among totalamounts of impurities in the first n-semiconductor layer 2 a, the firstp-semiconductor layer 2 b, the second n-semiconductor layer 3 a and thesecond p-semiconductor layer 3 b, when illustrated without taking thedegree of being large or small into consideration, become as shown inFIG. 5.

In forming the parallel p-n layer with the above-explained structure,the width of each of trenches for forming the first p-semiconductorlayer 2 b becomes equal to the width of each of trenches for forming thesecond p-semiconductor layer 3 b. This facilitates a process forcarrying out trench etching and a process for carrying out epitaxialgrowth of filling the trenches with the p-semiconductor layers to reducevariations in forming the parallel p-n layer.

The tenth embodiment is a vertical MOSFET chip in which, in the verticalMOSFET chip of the ninth embodiment, the impurity concentrations in thesecond p-semiconductor layer 3 b and the second n-semiconductor layer 3a in the second parallel p-n layer are made approximately equal to thosein the first p-semiconductor layer 2 b and the first n-semiconductorlayer 2 a in the first parallel p-n layer. The plane structure of theparallel p-n layer is the same as that shown in FIG. 15. Moreover, thecross sectional structure taken on the cutting line C-C in FIG. 15 isthe same as that shown in FIG. 16. Dimensions, impurity concentrationsand the like in all parts are, unless otherwise notified, the same asthose in the embodiment 9.

The distribution in the depth direction of each of the impurityconcentrations in the first p-semiconductor layer 2 b and the secondp-semiconductor layer 3 b is as shown in FIG. 6. Moreover, thedistribution in the depth direction of each of the impurityconcentrations in the first n-semiconductor layer 2 a and the secondn-semiconductor layer 3 a is as shown in FIG. 7. Furthermore, the valueNp0 of the impurity concentration in each of the first p-semiconductorlayer 2 b and the second p-semiconductor layer 3 b is approximatelyequal to the value Nn0 of the impurity concentration in each of thefirst n-semiconductor layer 2 a and the second n-semiconductor layer 3a, though the conductivity types of the impurities are different fromeach other. For example, all of the first p-semiconductor layer 2 b, thefirst n-semiconductor layer 2 a, the second p-semiconductor layer 3 band the second n-semiconductor layer 3 a have an impurity concentrationof the order of 4.5×10¹⁵ cm⁻³.

The relations of being large or small among total amounts of impuritiesin the first n-semiconductor layer 2 a, the first p-semiconductor layer2 b, the second n-semiconductor layer 3 a and the second p-semiconductorlayer 3 b, when illustrated without taking the degree of being large orsmall into consideration, become as shown in FIG. 17. However, FIG. 17only illustrates relations of large or small among total amounts ofimpurities in the semiconductor layers. Thus, the figure does notillustrate so far as how large or how small the total amounts ofimpurities are among them. The width of the first p-semiconductor layer2 b, that of the first n-semiconductor layer 2 a and that of the secondp-semiconductor layer 3 b are approximately equal to one another. Thus,the total amount of impurities in the first p-semiconductor layer 2 b,denoted by numeral 85, the total amount of impurities in the firstn-semiconductor layer 2 a, denoted by numeral 87, and the total amountof impurities in the second p-semiconductor layer 3 b, denoted bynumeral 86, become approximately equal to one another. While, the widthof the second n-semiconductor layer 3 a is smaller than that of thefirst n-semiconductor layer 2 a. Thus, the total amount of impurities inthe second n-semiconductor layer 3 a, denoted by numeral 88, becomessmaller than the total amount of impurities 87 in the firstn-semiconductor layer 2 a.

FIG. 18 is a partial plan view showing a principal section of a verticalMOSFET chip according to an eleventh embodiment of the invention. InFIG. 18, illustrations of the surface layer of the parallel p-n layerand surface structures of elements formed thereon are omitted. FIG. 19is a vertical cross sectional view showing a cross sectional structuretaken on the cutting line D-D traversing the active region and theinactive region in FIG. 18 in the direction perpendicular to thestripes.

As shown in FIG. 18 and FIG. 19, the eleventh embodiment is a verticalMOSFET chip in which, in the inactive region 230, the whole parallel p-nlayer in the section parallel to the stripes is made up of the secondparallel p-n layer with charges being in an unbalanced state. Along withthis, the width of the second p-semiconductor layer 3 b is made equal tothat of the first p-semiconductor layer 2 b. While, the width of thesecond n-semiconductor layer 3 a is made smaller than the width of thefirst n-semiconductor layer 2 a. The arrangements other than the above,dimensions, impurity concentrations and the like in all parts are thesame as those in the ninth embodiment.

The twelfth embodiment is a vertical MOSFET chip in which, in thevertical MOSFET chip of the eleventh embodiment, the impurityconcentrations in the second p-semiconductor layer 3 b and the secondn-semiconductor layer 3 a in the second parallel p-n layer are madeapproximately equal to those in the first p-semiconductor layer 2 b andthe first n-semiconductor layer 2 a in the first parallel p-n layer. Theplane structure of the parallel p-n layer is the same as that shown inFIG. 18. Moreover, the cross sectional structure taken on the cuttingline D-D in FIG. 18 is the same as that shown in FIG. 19. Dimensions,impurity concentrations and the like in all parts are, unless otherwisenotified, the same as those in the embodiment 11.

The distribution in the depth direction of each of the impurityconcentrations in the first p-semiconductor layer 2 b and the secondp-semiconductor layer 3 b is as shown in FIG. 6. Moreover, thedistribution in the depth direction of each of the impurityconcentrations in the first n-semiconductor layer 2 a and the secondn-semiconductor layer 3 a is as shown in FIG. 7. Furthermore, the valueNp0 of the impurity concentration in each of the first p-semiconductorlayer 2 b and the second p-semiconductor layer 3 b is approximatelyequal to the value Nn0 of the impurity concentration in each of thefirst n-semiconductor layer 2 a and the second n-semiconductor layer 3a, though the conductivity types of the impurities are different fromeach other.

For example, all of the first p-semiconductor layer 2 b, the firstn-semiconductor layer 2 a, the second p-semiconductor layer 3 b and thesecond n-semiconductor layer 3 a have an impurity concentration of theorder of 4.5×10¹⁵ cm⁻³. The relations of being large or small amongtotal amounts of impurities in the first n-semiconductor layer 2 a, thefirst p-semiconductor layer 2 b, the second n-semiconductor layer 3 aand the second p-semiconductor layer 3 b, when illustrated withouttaking the degree of being large or small into consideration, become asshown in FIG. 17.

The thirteenth embodiment is a vertical MOSFET chip in which, theimpurity concentration in the first p-semiconductor layer 2 b in thefirst parallel p-n layer and the impurity concentration in the secondp-semiconductor layer 3 b in the second parallel p-n layer are madehigher than those in the embodiment 9 to make the charges in the firstparallel p-n layer in an unbalanced state also in the active region 100.The plane structure of the parallel p-n layer is the same as that shownin FIG. 15. Moreover, the cross sectional structure taken on the cuttingline C-C in FIG. 15 is the same as that shown in FIG. 16. Dimensions,impurity concentrations and the like in all parts are, unless otherwisenotified, the same as those in the ninth embodiment.

The distribution in the depth direction of each of the impurityconcentrations in the first p-semiconductor layer 2 b and the secondp-semiconductor layer 3 b is as shown in FIG. 10. Moreover, thedistribution in the depth direction of each of the impurityconcentrations in the first n-semiconductor layer 2 a and the secondn-semiconductor layer 3 a is as shown in FIG. 11. The value Np0 of theimpurity concentration in the first p-semiconductor layer 2 b is higherthan the value Nn0 of the impurity concentration in the firstn-semiconductor layer 2 a, though the conductivity types of theimpurities are different from each other.

For example, the impurity concentrations in the first p-semiconductorlayer 2 b is on the order of 4.7×10¹⁵ cm⁻³, and the impurityconcentration in the first n-semiconductor layer 2 a is on the order of4.5×10¹⁵ cm⁻³. The impurity concentration in the second p-semiconductorlayer 3 b is on the order of 5.3×10¹⁵ cm⁻³, and the impurityconcentration in the second n-semiconductor layer 3 a is on the order of1.9×10¹⁵ cm⁻³. The relations of being large or small among total amountsof impurities in the first n-semiconductor layer 2 a, the firstp-semiconductor layer 2 b, the second n-semiconductor layer 3 a and thesecond p-semiconductor layer 3 b, when illustrated without taking thedegree of being large or small into consideration, become as shown inFIG. 12.

The fourteenth embodiment is a vertical MOSFET chip in which, in thevertical MOSFET chip of the thirteenth embodiment, the impurityconcentrations in the second p-semiconductor layer 3 b and the secondn-semiconductor layer 3 a in the second parallel p-n layer are madeapproximately equal to those in the first p-semiconductor layer 2 b andthe first n-semiconductor layer 2 a in the first parallel p-n layer,respectively. The plane structure of the parallel p-n layer is the sameas that shown in FIG. 15. Moreover, the cross sectional structure takenon the cutting line C-C in FIG. 15 is the same as that shown in FIG. 16.Dimensions, impurity concentrations and the like in all parts are,unless otherwise notified, the same as those in the thirteenthembodiment.

The distribution in the depth direction of each of the impurityconcentrations in the first p-semiconductor layer 2 b and the secondp-semiconductor layer 3 b is as shown in FIG. 13. Moreover, thedistribution in the depth direction of each of the impurityconcentrations in the first n-semiconductor layer 2 a and the secondn-semiconductor layer 3 a is as shown in FIG. 14. In addition, the valueNp0 of the impurity concentration in each of the first p-semiconductorlayer 2 b and the second p-semiconductor layer 3 b is higher than thevalue Nn0 of the impurity concentration in each of the firstn-semiconductor layer 2 a and the second n-semiconductor layer 3 a.

For example, both of the first p-semiconductor layer 2 b and the secondp-semiconductor layer 3 b have an impurity concentration of the order of4.7×10¹⁵ cm⁻³. Both of the first n-semiconductor layer 2 a and thesecond n-semiconductor layer 3 a have an impurity concentration of theorder of 4.5×10¹⁵ cm⁻³.

The relations of being large or small among total amounts of impuritiesin the first n-semiconductor layer 2 a, the first p-semiconductor layer2 b, the second n-semiconductor layer 3 a and the second p-semiconductorlayer 3 b, when illustrated without taking the degree of being large orsmall into consideration, become as shown in FIG. 20. However, FIG. 20only illustrates relations of large or small among total amounts ofimpurities in the semiconductor layers. Thus, the figure does notillustrate so far as how large or how small the total amounts ofimpurities are among them.

In the first p-semiconductor layer 2 b and the first n-semiconductorlayer 2 a, their widths are approximately equal to each other, while theimpurity concentrations in them differ from each other. Thus, the totalamount of impurities in the first p-semiconductor layer 2 b, denoted bynumeral 95, becomes larger than the total amount of impurities in thefirst n-semiconductor layer 2 a, denoted by numeral 97. The width of thefirst p-semiconductor layer 2 b and that of the second p-semiconductorlayer 3 b are approximately equal to each other. Thus, the total amountof impurities 95 in the first p-semiconductor layer 2 b and the totalamount of impurities in the second p-semiconductor layer 3 b, denoted bynumeral 96, become approximately equal to each other. While, the widthof the second n-semiconductor layer 3 a is smaller than that of thefirst n-semiconductor layer 2 a. Thus, the total amount of impurities inthe second n-semiconductor layer 3 a, denoted by numeral 98, becomessmaller than the total amount of impurities 97 in the firstn-semiconductor layer 2 a.

The fifteenth embodiment is a vertical MOSFET chip in which, in thevertical MOSFET chip of the eleventh embodiment, the whole parallel p-nlayer in the section parallel to the stripes in the inactive region 230is made up of the second parallel p-n layer with charges being in anunbalanced state. The plane structure of the parallel p-n layer is thesame as that shown in FIG. 18. Moreover, the cross sectional structuretaken on the cutting line D-D in FIG. 18 is the same as that shown inFIG. 19. Dimensions, impurity concentrations and the like in all partsare, unless otherwise notified, the same as those in the eleventhembodiment.

The sixteenth embodiment is a vertical MOSFET chip in which, in thevertical MOSFET chip of the eleventh embodiment, the whole parallel p-nlayer in the section parallel to the stripes in the inactive region 230is made up of the second parallel p-n layer with charges being in anunbalanced state. Along with this, the impurity concentrations in thesecond p-semiconductor layer 3 b and the second n-semiconductor layer 3a in the second parallel p-n layer are made approximately equal to thosein the first p-semiconductor layer 2 b and the first n-semiconductorlayer 2 a in the first parallel p-n layer, respectively. The planestructure of the parallel p-n layer is the same as that shown in FIG.18. Moreover, the cross sectional structure taken on the cutting lineD-D in FIG. 18 is the same as that shown in FIG. 19. Dimensions,impurity concentrations and the like in all parts are, unless otherwisenotified, the same as those in the eleventh embodiment.

The distribution in the depth direction of each of the impurityconcentrations in the first p-semiconductor layer 2 b and the secondp-semiconductor layer 3 b is as shown in FIG. 13. Moreover, thedistribution in the depth direction of each of the impurityconcentrations in the first n-semiconductor layer 2 a and the secondn-semiconductor layer 3 a is as shown in FIG. 14. In addition, the valueNp0 of the impurity concentration in each of the first p-semiconductorlayer 2 b and the second p-semiconductor layer 3 b is higher than thevalue Nn0 of the impurity concentration in each of the firstn-semiconductor layer 2 a and the second n-semiconductor layer 3 a.

For example, both of the first p-semiconductor layer 2 b and the secondp-semiconductor layer 3 b have an impurity concentration of the order of4.7×10¹⁵ cm⁻³. Both of the first n-semiconductor layer 2 a and thesecond n-semiconductor layer 3 a have an impurity concentration of theorder of 4.5×10¹⁵ cm⁻³. Moreover, the relations of being large or smallamong total amounts of impurities in the first n-semiconductor layer 2a, the first p-semiconductor layer 2 b, the second n-semiconductor layer3 a and the second p-semiconductor layer 3 b, when illustrated withouttaking the degree of being large or small into consideration, become asshown in FIG. 20.

FIG. 21 is a partial plan view showing a principal section of a verticalMOSFET chip according to an embodiment 17 of the invention. In FIG. 21,illustrations of the surface layer of the parallel p-n layer and surfacestructures of elements formed thereon are omitted. FIG. 22 is a verticalcross sectional view showing a cross sectional structure taken on thecutting line E-E traversing the active region and the inactive region inFIG. 21 in the direction perpendicular to the stripes.

As shown in FIG. 21 and FIG. 22, the seventeenth embodiment is avertical MOSFET chip in which, in the second parallel p-n layer in thesection parallel to the stripes in the inactive region 240, thedimension Wne of the width of the second n-semiconductor layer 3 a andthe dimension Wpe of the width of the second p-semiconductor layer 3 bare made smaller than the dimension Wna of the width of the firstn-semiconductor layer 2 a and the dimension Wpa of the width of thefirst p-semiconductor layer 2 b in the active region, respectively.Furthermore, the dimension Wne of the width of the secondn-semiconductor layer 3 a is made smaller than the dimension Wpe of thewidth of the second p-semiconductor layer 3 b to bring the charges inthe second parallel p-n layer to be in an unbalanced state.

In FIG. 23, there are schematically shown the relations among the widthsof the n-semiconductor layers 2 a and 3 a and the p-semiconductor layers2 b and 3 b in the parallel p-n layer. As shown in FIG. 23, in theembodiment 17, the dimension Wpa of the width of the firstp-semiconductor layer 2 b, denoted by numeral 105, and the dimension Wnaof the width of the first n-semiconductor layer 2 a, denoted by numeral107, are equal to each other. The dimension Wpe of the width of thesecond p-semiconductor layer 3 b, denoted by numeral 106, is smallerthan the dimension Wpa of the width of the first p-semiconductor layer 2b and the dimension Wna of the width of the first n-semiconductor layer2 a. The dimension Wne of the width of the second n-semiconductor layer3 a, denoted by numeral 108, is smaller than the dimension Wpe of thewidth of the second p-semiconductor layer 3 b.

Therefore, in the second parallel p-n layer, the state of interdiffusionof impurities between the second n-semiconductor layer 3 a and thesecond p-semiconductor layer 3 b is made different from that in thefirst embodiment. This makes impurity concentrations in both of thesecond n-semiconductor layer 3 a and the second p-semiconductor layer 3b different from those in the first embodiment. The arrangements otherthan the above, dimensions, impurity concentrations and the like in allparts are, unless otherwise notified, the same as those in the firstembodiment.

FIG. 24 is a diagram showing impurity concentration distributions in thedepth direction in the p-semiconductor layers of the semiconductordevice according to the embodiment 17. As shown in FIG. 24, both of theimpurity concentration distribution in the depth direction in the firstp-semiconductor layer 2 b, denoted by numeral 111, and the impurityconcentration distribution in the depth direction in the secondp-semiconductor layer 3 b, denoted by numeral 112, are uniform.Moreover, the value Np1 of the impurity concentration in the secondp-semiconductor layer 3 b is lower than the value Np0 of the impurityconcentration in the first p-semiconductor layer 2 b. Furthermore, FIG.25 is a diagram showing impurity concentration distributions in thedepth direction in the n-semiconductor layers of the semiconductordevice according to the seventeenth embodiment. As shown in FIG. 25, theimpurity concentration distribution in the depth direction in the firstn-semiconductor layer 2 a, denoted by numeral 113, and the impurityconcentration distribution in the depth direction in the secondn-semiconductor layer 3 a, denoted by numeral 114, are uniform. Inaddition, the value Nn1 of the impurity concentration in the secondn-semiconductor layer 3 a is lower than the value Nn0 of the impurityconcentration in the first n-semiconductor layer 2 a. The value Np0 ofthe impurity concentration in the first p-semiconductor layer 2 b isapproximately equal to the value Nn0 of the impurity concentration inthe first n-semiconductor layer 2 a, though the conductivity types ofthe impurities are different from each other.

For example, the impurity concentrations in the second p-semiconductorlayer 3 b is on the order of 3.5×10¹⁵ cm⁻³, and the impurityconcentration in the second n-semiconductor layer 3 a is on the order of2.0×10¹⁵ cm⁻³. Moreover, the width of the second n-semiconductor layer 3a is about 2.5 μm, and the width of the second p-semiconductor layer 3 bis about 3.5 μm.

In the first p-semiconductor layer 2 b and the first n-semiconductorlayer 2 a, both of their widths and impurity concentrations areapproximately equal to each other. Thus, the total amount of impuritiesin the first p-semiconductor layer 2 b, denoted by numeral 115, and thetotal amount of impurities in the first n-semiconductor layer 2 a,denoted by numeral 117, become approximately equal to each other. While,the width of the second p-semiconductor layer 3 b is smaller than thatof the first p-semiconductor layer 2 b, and the impurity concentrationin the second p-semiconductor layer 3 b is lower than the impurityconcentration in the first p-semiconductor layer 2 b. Thus, the totalamount of impurities in the second p-semiconductor layer 3 b, denoted bynumeral 116, becomes smaller than the total amount of impurities 115 inthe first p-semiconductor layer 2 b.

Moreover, the width of the second n-semiconductor layer 3 a is smallerthan that of the first n-semiconductor layer 2 a, and the impurityconcentration in the second n-semiconductor layer 3 a is lower than thatin the first n-semiconductor layer 2 a. Thus, the total amount ofimpurities in the second n-semiconductor layer 3 a, denoted by numeral118, becomes smaller than the total amount of impurities 117 in thefirst n-semiconductor layer 2 a. Furthermore, the width of the secondn-semiconductor layer 3 a is smaller than that of the secondp-semiconductor layer 3 b, and the impurity concentration in the secondn-semiconductor layer 3 a is lower than that in the secondp-semiconductor layer 3 b. Thus, the total amount of impurities 118 inthe second n-semiconductor layer 3 a becomes smaller than the totalamount of impurities 116 in the second p-semiconductor layer 3 b.However, FIG. 26 only illustrates relations of large or small amongtotal amounts of impurities in the semiconductor layers. Thus, thefigure does not illustrate so far as how large or how small the totalamounts of impurities are among them.

According to the embodiment 17, in the parallel p-n layer located on theoutside of the end of the source electrode 10, the widths of the secondn-semiconductor layer 3 a and the second p-semiconductor layer 3 b aresmaller than the widths of the first n-semiconductor layer 2 a and thefirst p-semiconductor layer 2 b in the active region 100, respectively.This makes a depletion layer liable to expand to easily ensure a highbreakdown voltage. Since the width of the second n-semiconductor layer 3a is smaller than the widths of the first n-semiconductor layer 2 a, theimpurity concentration becomes higher and the total amount of impuritiesbecomes larger in the second p-semiconductor layer 3 b compared withthose in the second n-semiconductor layer 3 a. Therefore, the secondp-semiconductor layer 3 b performs a role of expanding a depletion layeroutward like a guard ring to more easily ensure a high breakdownvoltage.

Moreover, compared with a structure in which the width of the secondp-semiconductor layer 3 b is larger than that of the firstp-semiconductor layer 2 b, the structure according to the seventeenthembodiment provides the second p-semiconductor layer 3 b a loweredimpurity concentration. This suppresses expansion of the depletion layerto some extent, by which a width necessary for the voltage withstandingstructure section can be shortened. Furthermore, since the charges inthe parallel p-n layer laid out in the voltage withstanding structuresection in the inactive region 240 are in an unbalanced state, it isconsidered that the breakdown voltage of the section directly below thesource electrode 10 is lowered. However, the interlayer insulator film 9b provided directly below the source electrode 10 withstands the voltageequivalent to the lowered portion of the breakdown voltage to cause nolowering in the breakdown voltage in total. In addition, when thestructure of the vertical MOSFET chip according to the embodiment 17 isformed by the trench filling method, in the inactive region 240, thetrench for forming the second p-semiconductor layer 3 b is provided withthe width larger than that of the second n-semiconductor layer 3 a.Therefore, the aspect ratio of the trench is made lower by an amountcorresponding to the increase in the width than in the case in which thewidths of the layer 3 b and the layer 3 a are made equal to each other.This reduces the degree of difficulty of the process, that is,facilitates the manufacture.

The eighteenth embodiment is a vertical MOSFET chip in which, in thevertical MOSFET chip of the seventeenth embodiment, the impurityconcentrations in the second p-semiconductor layer 3 b and the secondn-semiconductor layer 3 a in the second parallel p-n layer are madeapproximately equal to those in the first p-semiconductor layer 2 b andthe first n-semiconductor layer 2 a in the first parallel p-n layer. Theplane structure of the parallel p-n layer is the same as that shown inFIG. 21. Moreover, the cross sectional structure taken on the cuttingline E-E in FIG. 21 is the same as that shown in FIG. 22. Dimensions,impurity concentrations and the like in all parts are, unless otherwisenotified, the same as those in the seventeenth embodiment.

The distribution in the depth direction of the impurity concentration inthe first p-semiconductor layer 2 b, denoted by numeral 121, and thedistribution in the depth direction of the second p-semiconductor layer3 b, denoted by numeral 122, are as shown in FIG. 27. Moreover, thedistribution in the depth direction of the impurity concentrations inthe first n-semiconductor layer 2 a, denoted by numeral 123, and thedistribution in the depth direction of the second n-semiconductor layer3 a, denoted by numeral 124, are as shown in FIG. 28. Furthermore, thevalue Np0 of the impurity concentration in the first p-semiconductorlayer 2 b, the value Np1 of the impurity concentration in the secondp-semiconductor layer 3 b, the value Nn0 of the impurity concentrationin the first n-semiconductor layer 2 a and the value Nn1 of the impurityconcentration in the second n-semiconductor layer 3 a are approximatelyequal to one another, though the conductivity types of the impuritiesare different from one another. For example, all of the firstp-semiconductor layer 2 b, the first n-semiconductor layer 2 a, thesecond p-semiconductor layer 3 b and the second n-semiconductor layer 3a have an impurity concentration of the order of 4.5×10¹⁵ cm⁻³.

Such impurity concentration distributions, as was explained also in thedescription of the second embodiment, can be achieved by forming theelement surface structures of the MOSFET under a low temperatureprocess. This makes the impurity concentrations in the n-semiconductorlayers and the p-semiconductor layers in the parallel p-n layerapproximately equal to those of the substrate and the epitaxial layersfilling the trenches, respectively, even though the widths of thep-semiconductor layers and the n-semiconductor layers in the parallelp-n layer differ from one another.

The relations of being large or small among total amounts of impuritiesin the first n-semiconductor layer 2 a, the first p-semiconductor layer2 b, the second n-semiconductor layer 3 a and the second p-semiconductorlayer 3 b, when illustrated without taking the degree of being large orsmall into consideration, become as shown in FIG. 26. The width of thefirst p-semiconductor layer 2 b and that of the first n-semiconductorlayer 2 a are approximately equal to each other. Thus, the total amountof impurities 115 in the first p-semiconductor layer 2 b and the totalamount of impurities 117 in the first n-semiconductor layer 2 a becomeapproximately equal to each other. While, the width of the secondp-semiconductor layer 3 b is smaller than the width of the firstp-semiconductor layer 2 b. Thus, the total amount of impurities 116 inthe second p-semiconductor layer 3 b becomes smaller than the totalamount of impurities 115 in the first p-semiconductor layer 2 b.

Moreover, the width of the second n-semiconductor layer 3 a is smallerthan the width of the first n-semiconductor layer 2 a. Thus, the totalamount of impurities 118 in the second n-semiconductor layer 3 a becomessmaller than the total amount of impurities 117 in the firstn-semiconductor layer 2 a. Furthermore, the width of the secondn-semiconductor layer 3 a is smaller than the width of the secondp-semiconductor layer 3 b. Thus, the total amount of impurities 118 inthe second n-semiconductor layer 3 a becomes smaller than the totalamount of impurities 116 in the second p-semiconductor layer 3 b.According to the eighteenth embodiment, no interdiffusion of impuritiesdue to heat history occurs to facilitate the control of the impurityconcentrations in the parallel p-n layer. This therefore enables almostdirect realization of a structure determined by performing numericalcalculations such as computer simulations.

FIG. 29 is a partial plan view showing a principal section of a verticalMOSFET chip according to an embodiment 19 of the invention. In FIG. 29,illustrations of the surface layer of the parallel p-n layer and surfacestructures of elements formed thereon are omitted. FIG. 30 is a verticalcross sectional view showing a cross sectional structure taken on thecutting line F-F traversing the active region and the inactive region inFIG. 29 in the direction perpendicular to the stripes.

As shown in FIG. 29 and FIG. 30, the nineteenth embodiment is a verticalMOSFET chip in which, in the inactive region 250, the whole parallel p-nlayer in the section parallel to the stripes is made up of the secondparallel p-n layer with charges being in an unbalanced state. Inparticular, in a portion of the inactive region 250 in the proximity ofthe boundary with the active region 100, the second parallel p-n layeris laid out also in a portion where the source electrode 10 is incontact with the semiconductor surface, that is, in a portion withoutthe interlayer insulator film 9 b. The arrangements other than theabove, dimensions, impurity concentrations and the like in all parts arethe same as those in the embodiment 17.

According to the nineteenth embodiment, like in the third embodiment,the breakdown voltage in the depth direction is lowered in the secondparallel p-n layer with unbalanced charges. Thus, an avalanche occurs ata portion at which the source electrode 10 is in contact with thesemiconductor surface in the inactive region 250. Therefore, comparedwith the case in which avalanche breakdown occurs below the interlayerinsulator film 9 b, an avalanche current is efficiently pulled out fromthe source electrode 10 to cause no concentration of current, whichenhances avalanche durability.

The twentieth embodiment is a vertical MOSFET chip in which, in thevertical MOSFET chip of the nineteenth embodiment, the impurityconcentrations in the second p-semiconductor layer 3 b and the secondn-semiconductor layer 3 a in the second parallel p-n layer are madeapproximately equal to those in the first p-semiconductor layer 2 b andthe first n-semiconductor layer 2 a in the first parallel p-n layer. Theplane structure of the parallel p-n layer is the same as that shown inFIG. 29. Moreover, the cross sectional structure taken on the cuttingline F-F in FIG. 29 is the same as that shown in FIG. 30. Dimensions,impurity concentrations and the like in all parts are, unless otherwisenotified, the same as those in the nineteenth embodiment.

The distribution in the depth direction of each of the impurityconcentrations in the first p-semiconductor layer 2 b and the secondp-semiconductor layer 3 b is as shown in FIG. 27. Moreover, thedistribution in the depth direction of each of the impurityconcentrations in the first n-semiconductor layer 2 a and the secondn-semiconductor layer 3 a is as shown in FIG. 28. Furthermore, the valueNp0 of the impurity concentration in the first p-semiconductor layer 2b, the value Np1 of the impurity concentration in the secondp-semiconductor layer 3 b, the value Nn0 of the impurity concentrationin the first n-semiconductor layer 2 a and the value Nn1 of the impurityconcentration in the second n-semiconductor layer 3 a are approximatelyequal to one another, though the conductivity types of the impuritiesare different from one another, with a value, for example, of the orderof 4.5×10¹⁵ cm⁻³.

The relations of being large or small among total amounts of impuritiesin the first n-semiconductor layer 2 a, the first p-semiconductor layer2 b, the second n-semiconductor layer 3 a and the second p-semiconductorlayer 3 b, when illustrated without taking the degree of being large orsmall into consideration, become as shown in FIG. 26. According to thetwentieth embodiment, like in the eighteenth embodiment and thenineteenth embodiment, the impurity concentrations are easily controlledto enhance avalanche durability.

The twenty-first embodiment is a vertical MOSFET chip in which, theimpurity concentration in the first p-semiconductor layer 2 b in thefirst parallel p-n layer and the impurity concentration in the secondp-semiconductor layer 3 b in the second parallel p-n layer are madehigher than those in the embodiment 17 to make the charges in the firstparallel p-n layer in an unbalanced state also in the active region 100.The plane structure of the parallel p-n layer is the same as that shownin FIG. 21. Moreover, the cross sectional structure taken on the cuttingline E-E in FIG. 21 is the same as that shown in FIG. 22. Dimensions,impurity concentrations and the like in all parts are, unless otherwisenotified, the same as those in the seventeenth embodiment.

FIG. 31 is a diagram showing impurity concentration distributions in thedepth direction in the p-semiconductor layers of the semiconductordevice according to the embodiment 21. As shown in FIG. 31, both of theimpurity concentration distribution in the depth direction in the firstp-semiconductor layer 2 b, denoted by numeral 131, and the impurityconcentration distribution in the depth direction in the secondp-semiconductor layer 3 b, denoted by numeral 132, are uniform.Moreover, the value Np1 of the impurity concentration in the secondp-semiconductor layer 3 b is lower than the value Np0 of the impurityconcentration in the first p-semiconductor layer 2 b. Furthermore, FIG.32 is a diagram showing impurity concentration distributions in thedepth direction in the n-semiconductor layers of the semiconductordevice according to the embodiment 21. As shown in FIG. 32, the impurityconcentration distribution in the depth direction in the firstn-semiconductor layer 2 a, denoted by numeral 133, and the impurityconcentration distribution in the depth direction in the secondn-semiconductor layer 3 a, denoted by numeral 134, are uniform.

In addition, the value Nn1 of the impurity concentration in the secondn-semiconductor layer 3 a is lower than the value Nn0 of the impurityconcentration in the first n-semiconductor layer 2 a. Furthermore, thevalue Np0 of the impurity concentration in the first p-semiconductorlayer 2 b and the value Np1 of the impurity concentration in the secondp-semiconductor layer 3 b are higher than the value Nn0 of the impurityconcentration in the first n-semiconductor layer 2 a and the impurityconcentration Nn1 in the second n-semiconductor layer 3 a, respectively,though the conductivity types of the impurities are different from oneanother.

For example, the impurity concentrations in the first p-semiconductorlayer 2 b is on the order of 4.7×10¹⁵ cm⁻³, and the impurityconcentration in the first n-semiconductor layer 2 a is on the order of4.5×10¹⁵ cm⁻³. The impurity concentration in the second p-semiconductorlayer 3 b is on the order of 3.7×10¹⁵ cm⁻³, and the impurityconcentration in the second n-semiconductor layer 3 a is on the order of2.0×10¹⁵ cm⁻³.

The relations of being large or small among total amounts of impuritiesin the first n-semiconductor layer 2 a, the first p-semiconductor layer2 b, the second n-semiconductor layer 3 a and the second p-semiconductorlayer 3 b, when illustrated without taking the degree of being large orsmall into consideration, become as shown in FIG. 33. However, FIG. 33only illustrates relations of large or small among total amounts ofimpurities in the semiconductor layers. Thus, the figure does notillustrate so far as how large or how small the total amounts ofimpurities are among them.

In the first p-semiconductor layer 2 b and the first n-semiconductorlayer 2 a, their widths are approximately equal to each other, while theimpurity concentrations in them differ from each other. Thus, the totalamount of impurities in the first p-semiconductor layer 2 b, denoted bynumeral 135, becomes larger than the total amount of impurities in thefirst n-semiconductor layer 2 a, denoted by numeral 137. Moreover, thewidth of the second p-semiconductor layer 3 b is smaller than that ofthe first p-semiconductor layer 2 b, and the impurity concentration inthe second p-semiconductor layer 3 b is lower than that in the firstp-semiconductor layer 2 b. Thus, the total amount of impurities in thesecond p-semiconductor layer 3 b, denoted by numeral 136, becomessmaller than the total amount of impurities 135 in the firstp-semiconductor layer 2 b.

Furthermore, the width of the second n-semiconductor layer 3 a issmaller than that of the first n-semiconductor layer 2 a, and theimpurity concentration in the second n-semiconductor layer 3 a is lowerthan that in the first n-semiconductor layer 2 a. Thus, the total amountof impurities in the second n-semiconductor layer 3 a, denoted bynumeral 138, becomes smaller than the total amount of impurities 137 inthe first n-semiconductor layer 2 a. In addition, the width of thesecond n-semiconductor layer 3 a is smaller than that of the secondp-semiconductor layer 3 b, and the impurity concentration in the secondn-semiconductor layer 3 a is lower than that in the secondp-semiconductor layer 3 b. Thus, the total amount of impurities 138 inthe second n-semiconductor layer 3 a becomes smaller than the totalamount of impurities 136 in the second p-semiconductor layer 3 b.

According to the twenty-first embodiment, in the inactive region 240,the impurity concentration in the second p-semiconductor layer 3 b ishigher than that in the seventeenth embodiment and the total amount ofimpurities in the second p-semiconductor layer 3 b is larger than thatin the seventeenth embodiment. Thus, a depletion layer is made to expandin the inactive region 240 more easily than in the seventeenthembodiment. This increases a breakdown voltage in the inactive region240 to become close to the breakdown voltage in the active region 100.Thus, avalanche breakdown becomes liable to occur in the active region100. Therefore, concentration of an avalanche current becomes hard tooccur to enhance avalanche durability. Moreover, the impurityconcentration made higher in the first p-semiconductor layer 2 b in theactive region 100 suppresses negative resistance component even though ahole current is accumulated when an avalanche current is generated. Thisfurther enhances avalanche durability.

The twenty-second embodiment is a vertical MOSFET chip in which, in thevertical MOSFET chip of the embodiment 21, the impurity concentrationsin the second p-semiconductor layer 3 b and the second n-semiconductorlayer 3 a in the second parallel p-n layer are made approximately equalto those in the first p-semiconductor layer 2 b and the firstn-semiconductor layer 2 a in the first parallel p-n layer, respectively.The plane structure of the parallel p-n layer is the same as that shownin FIG. 21. Moreover, the cross sectional structure taken on the cuttingline E-E in FIG. 21 is the same as that shown in FIG. 22. Dimensions,impurity concentrations and the like in all parts are, unless otherwisenotified, the same as those in the twenty-first embodiment.

The distribution in the depth direction of the impurity concentration inthe first p-semiconductor layer 2 b, denoted by numeral 141, and thedistribution in the depth direction of the impurity concentration in thesecond p-semiconductor layer 3 b, denoted by numeral 142, are as shownin FIG. 34. Moreover, the distribution in the depth direction of theimpurity concentrations in the first n-semiconductor layer 2 a, denotedby numeral 143, and the distribution in the depth direction of theimpurity concentrations in the second n-semiconductor layer 3 a, denotedby numeral 144, are as shown in FIG. 35. In addition, the value Np0 ofthe impurity concentration in the first p-semiconductor layer 2 b andthe value Np1 of the impurity concentration in the secondp-semiconductor layer 3 b are higher than the value Nn0 of the impurityconcentration in the first n-semiconductor layer 2 a and the value Nn1of the impurity concentration in the second n-semiconductor layer 3 a,though the conductivity types of the impurities are different from oneanother.

For example, both of the first p-semiconductor layer 2 b and the secondp-semiconductor layer 3 b have an impurity concentration of the order of4.7×10¹⁵ cm⁻³. Both of the first n-semiconductor layer 2 a and thesecond n-semiconductor layer 3 a have an impurity concentration of theorder of 4.5×10¹⁵ cm⁻³. Such impurity concentration distributions, aswas explained also in the description of the embodiment 2, can beachieved by forming the element surface structures of the MOSFET under alow temperature process.

The relations of being large or small among total amounts of impuritiesin the first n-semiconductor layer 2 a, the first p-semiconductor layer2 b, the second n-semiconductor layer 3 a and the second p-semiconductorlayer 3 b, when illustrated without taking the degree of being large orsmall into consideration, become as shown in FIG. 33. According to thetwenty-second embodiment, the same advantage as that of the twenty-firstembodiment can be obtained. Moreover, like in the eighteenth embodiment,no interdiffusion of impurities due to heat history occurs to facilitatethe control of the impurity concentrations in the parallel p-n layer.

The twenty-third embodiment is a vertical MOSFET chip in which, in thevertical MOSFET chip of the embodiment 21, the whole parallel p-n layerin the section parallel to the stripes in the inactive region 250 ismade up of the second parallel p-n layer with charges being in anunbalanced state. The plane structure of the parallel p-n layer is thesame as that shown in FIG. 29. Moreover, the cross sectional structuretaken on the cutting line F-F in FIG. 29 is the same as that shown inFIG. 30. Dimensions, impurity concentrations and the like in all partsare, unless otherwise notified, the same as those in the embodiment 21.According to the twenty-third embodiment, the same advantage as that ofthe twenty-first embodiment can be obtained. Furthermore, the sameadvantage as that of the nineteenth embodiment can be obtained.

The twenty-forth embodiment is a vertical MOSFET chip in which, in thevertical MOSFET chip of the embodiment 22, the whole parallel p-n layerin the section parallel to the stripes in the inactive region 250 ismade up of the second parallel p-n layer with charges being in anunbalanced state. The plane structure of the parallel p-n layer is thesame as that shown in FIG. 29. Moreover, the cross sectional structuretaken on the cutting line F-F in FIG. 29 is the same as that shown inFIG. 30. Dimensions, impurity concentrations and the like in all partsare, unless otherwise notified, the same as those in the twenty-secondembodiment. According to the twenty-fourth embodiment, the sameadvantage as that of the twenty-second embodiment can be obtained.Furthermore, the same advantage as that of the twentieth embodiment canbe obtained.

The twenty-fifth embodiment is a method of manufacturing a semiconductordevice which can be applied when manufacturing the semiconductor deviceaccording to the above-explained first, third, fifth or seventhembodiments. FIGS. 36 to 41 are cross sectional views showing respectivestructures of the semiconductor device in the main steps in itsmanufacturing process. First, an n-type low resistance semiconductorsubstrate is prepared which becomes an n⁺⁺-drain layer 1. At this time,the direction of crystal plane of the semiconductor substrate is takenas the (100)-plane or equivalent to this. Moreover, the impurityconcentration of the semiconductor substrate is taken as on the order of2.0×10¹⁸ cm⁻³. On the prepared semiconductor substrate, an n-epitaxiallayer 31 is formed with a thickness of about 50 μm. The impurityconcentration of the n-epitaxial layer 31 is taken as on the order of6.0×10¹⁵ cm⁻³. A state up to this is shown in FIG. 36.

Next to this, an oxide film (or an insulator film such as a nitridefilm) 32, becoming a hard mask for trench etching, is formed with athickness of 1.6 μm or more, for example, 2.4 μm. The thickness of theoxide film 32 is appropriately selected on the basis of the selectivityfor the oxide film and silicon in trench etching so that the oxide filmis left even though trenches with desired depth are formed. For example,when trenches each with a depth of about 50 μm are formed, an oxide filmwith a thickness of the order of 2.4 μm is left with a sufficientthickness even after the trench etching.

Then, patterning of the oxide film 32 is carried out by lithography toform hard masks. For the region in which the first parallel p-n layer islaid out, each opening width in the oxide film 32 is taken as, forexample, 5 μm and each width of the oxide film 32 between the openingsis taken as 5 μm, for example. In other words, the hard masks eachhaving the width of 5 μm are spaced 5 μm apart, for example. The regionin which the first parallel p-n layer is laid out includes, in theembodiment 1 and the embodiment 5, the regions to become the activeregion 100, a part of the section parallel to the stripes in theinactive region 200 and the section perpendicular to the stripes in theinactive region 200. Moreover, in the embodiment 3 and the embodiment 7,the region includes the regions to become the active region 100 and thesection perpendicular to the stripes in the inactive region 210.

Meanwhile, for the region in which the second parallel p-n layer is laidout, each opening width in the oxide film 32 is enlarged. Along withthis, each width of the oxide film 32 between the openings is reduced.Specifically, for example, with each opening width in the oxide film 32taken as 6 μm and each width of the oxide film 32 between the openingstaken as 4 μm, hard masks each having the width of 4 μm are spaced 6 μmapart. The region in which the second parallel p-n layer is laid out is,in the embodiment 1 and the embodiment 5, the region to become a part ofthe section parallel to the stripes in the inactive region 200.Moreover, in the embodiment 3 and the embodiment 7, the region includesthe whole region to become the section parallel to the stripes in theinactive region 210.

Following this, trench etching is carried out to form in the epitaxiallayer 31 trenches having a depth of about 50 μm, trenches 33 a having anopening width of 5 μm and trenches 33 b having an opening width of 6 μm,for example. At this time, the trenches 33 a and 33 b are formed so thatthe direction of crystal plane of the side face of each of the formedtrenches becomes the (010)-plane or a plane equivalent to this. Aboutthe hard masks for the trenches, they are also patterned so that thetrenches 33 a and 33 b are formed with the trench side faces each havingsuch direction of crystal plane. The state up to this is shown in FIG.37.

Then, the trenches 33 a and 33 b, each with the side face having suchdirection of crystal plane, are filled with boron-doped p-epitaxiallayers 34 a and 34 b, respectively. The impurity concentration in eachof the p-epitaxial layers 34 a and 34 b is, in the first embodiment andthe third embodiment, on the order of 6.0×10¹⁵ cm⁻³, for example, and inthe fifth embodiment and the seventh embodiment, on the order of6.3×10¹⁵ cm⁻³, for example. The p-epitaxial layers 34 a and 34 b aremade grown until they become to have a thickness equal to or more thanone-half the opening width of the trench 33 b having the larger width.For example, the time for carrying out the epitaxial growth is taken asthe time required for the p-epitaxial layers 34 a and 34 b grown to athickness of 4 μm.

This enables the p-epitaxial layers 34 b not only to fill the trenches33 b, each having the larger opening width, with no void being presentedbut also to be made grown to a level above the level of the surfaces ofthe oxide films 32 after the trenches 33 b are formed. This is similarto the trenches 33 a each having the smaller opening width. In thetrenches 33 a, the p-epitaxial layers 34 a are made grown with no voidbeing presented to fill the trenches 33 a and to be further made grownto a level above the level of the surfaces of the oxide films 32 afterthe trenches 33 a are formed. The p-epitaxial layers 34 a, filling thetrenches 33 a each having the smaller opening width, are grown higherthan the p-epitaxial layers 34 b filling the trenches 33 b each havingthe larger opening width. In this way, there are variations in thethicknesses of the p-epitaxial layers 34 a and 34 b grown above thesurfaces of the oxide films 32. The variations, however, are removed inthe step of polishing such as CMP (Chemical Mechanical Polishing)carried out later. The state up to this is shown in FIG. 38.

The polishing step is first carried out with the oxide films 32, used asthe hard masks for the trench etching, also used as polishing stoppers.Thus, portions of the epitaxial layers 34 a and 34 b grown to the levelabove the level of the surfaces of the oxide films 32 are removed. Thepolishing step thus carried out can therefore eliminate variations inthe thicknesses of the p-epitaxial layers 34 a and 34 b caused bydifference in the opening width between the trench 33 a and the trench33 b. Hence, the variations occurred in the epitaxial process can beminimized. Therefore, even though the opening widths of the trench 33 aand the trench 33 b differ from each other, the parallel p-n layer canbe formed with a uniform depth. The state up to this is shown in FIG.39.

In the next, as shown in FIG. 40, the oxide films 32 are removed.Thereafter, mirror polishing of the surface is carried out to eliminateunevenness on the surface caused by the removal of the oxide films 32.The amount of polishing is, for example, on the order of 1.0 μm, thoughthe invention is not particularly limited to this. This is because thethickness of the oxide film 32 of the order of 0.5 μm is left after thepolishing is carried out with the oxide film 32 used as the polishingstopper. Therefore, the final length in the depth direction of theparallel p-n layer becomes on the order of 49 μm.

In this way, as shown in FIG. 41, a super-junction semiconductorsubstrate is completed which has the first parallel p-n layer and thesecond parallel p-n layer. The first parallel p-n layer includes thefirst n-semiconductor layers 2 a of the n-epitaxial layer 31 and thefirst p-semiconductor layers 2 b of the p-epitaxial layer 34 a beingalternately arranged. The second parallel p-n layer includes the secondn-semiconductor layers 3 a of the n-epitaxial layer 31 and the secondp-semiconductor layers 3 b of the p-epitaxial layer 34 a beingalternately arranged.

With the use of the super-junction semiconductor substrate, the elementsurface structure, the peripheral voltage withstanding structure, thedrain electrode and the like of the MOSFET are formed. At this time, thesurface structure is formed at relatively high temperatures, forexample, of the order of 1000 to 1100° C. This causes interdiffusion ofimpurities to complete the semiconductor device according to the first,third, fifth and seventh embodiments in which the second parallel p-nlayer and the first parallel layer differ from each other in impurityconcentrations. The second parallel p-n layer has the secondp-semiconductor layer 3 b with the larger width, and the first parallelp-n layer has the first p-semiconductor layer 2 b with the width equalto that of the first n-semiconductor layer 2 a. Since the processes ofmanufacturing the element surface structure, the peripheral voltagewithstanding structure and the like of the MOSFET are well-known, theexplanation about them will be omitted.

By applying the above-explained manufacturing method, it becomes onlynecessary to change the opening widths of a part of the trenches whenforming the trenches and to determine the thickness of the epitaxiallayer filling each of the trenches to the trench with the largestopening width. Therefore, compared with the case of forming the trencheswith the same width and the same spacing in all of the regions to becomethe active region and the inactive region, the semiconductor device canbe manufactured with little increase in cost. The oxide films 32 and theepitaxial layers 34 a and 34 b can be polished together to finish thesurface into the mirror surface without dividing the polishing step intothe polishing step of using the oxide films 32 as the polishing stoppersand the polishing step of carrying out mirror polishing of the surface.

The manufacturing method according to the twenty-fifth embodiment canalso be applied to the case of manufacturing the semiconductor deviceaccording to the above-explained seventeenth, nineteenth, twenty-firstand twenty-third embodiments. In the case, however, the width of thetrench 33 b, formed in the region where the second parallel p-n layer islaid out, is made smaller than that of the trench 33 a, formed in theregion where the first parallel p-n layer is laid out.

The twenty-sixth embodiment is a method of manufacturing a semiconductordevice that can be applied when manufacturing the semiconductor deviceaccording to the above-explained ninth, eleventh, thirteenth andfifteenth embodiments. FIGS. 42 to 46 are cross sectional views showingrespective structures of the semiconductor device in the main steps inits manufacturing process. First, like in the twenty-fifth embodiment,an n-type low resistance semiconductor substrate is prepared whichbecomes an n⁺⁺-drain layer 1. In the n-type low resistance semiconductorsubstrate, the direction of crystal plane is taken as the (100)-plane orequivalent to this and the impurity concentration of the semiconductorsubstrate is taken as on the order of 2.0×10¹⁸ cm⁻³. Moreover, as shownin FIG. 36, on the semiconductor substrate, an n-epitaxial layer 31 isformed with a thickness of about 50 μm. The impurity concentration ofthe n-epitaxial layer 31 is taken as on the order of 6.0×10¹⁵ cm⁻³.

Next to this, an oxide film (or an insulator film such as a nitridefilm) 32, becoming a hard mask for trench etching, is formed. Thethickness of the oxide film 32 is similar to that in the embodiment 25.Then, hard masks are formed by carrying out patterning of the oxide film32. For the region in which the first parallel p-n layer is laid out,the hard masks each having a width of 5 μm are spaced 5 μm apart, forexample. The region in which the first parallel p-n layer is laid outincludes, in the ninth embodiment and the thirteenth embodiment, theregions to become the active region 100, a part of the section parallelto the stripes in the inactive region 220 and the section perpendicularto the stripes in the inactive region 220. Moreover, in the eleventhembodiment and the fifteenth embodiment, the region includes the regionsto become the active region 100 and the section perpendicular to thestripes in the inactive region 230.

Meanwhile, for the region in which the second parallel p-n layer is laidout, hard masks each having the width of 3.5 μm are spaced 5 μm apart,for example. Thus, the spacing (pitch) between the arranged hard masksis different from that in the first parallel p-n layer. The region inwhich the second parallel p-n layer is laid out is, in the ninthembodiment and the thirteenth embodiment, the region to become a part ofthe section parallel to the stripes in the inactive region 220.Moreover, in the embodiment 11 and the embodiment 15, the region is thewhole region to become the section parallel to the stripes in theinactive region 230. Following this, trench etching is carried out toform in the epitaxial layer 31 trenches 33 c having a depth of about 50μm and an opening width of 5 μm, for example. Since all of the trenches33 c have the same opening widths, the depths of the trenches can beeasily controlled. The direction of crystal plane of the side face ofeach of the trenches is the same as that in the twenty-fifth embodiment.The state up to this is shown in FIG. 42.

Then, the trenches 33 c are filled with boron-doped p-epitaxial layers34 c with the p-epitaxial layers 34 c made grown to a thickness of onehalf or more the opening width of the trench 33 c. In this case, thep-epitaxial layer 34 c filling each of the trenches 33 c is grown to aheight approximately equal to the others which height is above thesurfaces of the oxide films 32 after the trenches were formed. Theimpurity concentration in each of the p-epitaxial layers 34 c is, in theninth embodiment and the eleventh embodiment, on the order of 6.0×10¹⁵cm⁻³, for example, and in the embodiment 13 and the embodiment 15, onthe order of 6.3×10¹⁵ cm⁻³, for example. The state up to this is shownin FIG. 43.

Following this, polishing is carried out. The polishing is first carriedout with the oxide films 32 used as polishing stoppers. Thus, portionsof the epitaxial layers 34 c grown to the level above the level of thesurfaces of the oxide films 32 are removed. At this time, since thep-epitaxial layers 34 c are grown to heights approximately equal to oneanother, variations in heights in polishing the p-epitaxial layers 34 ccan be reduced. Therefore, the parallel p-n layer can be formed with auniform depth. The state up to this is shown in FIG. 44.

In the next, as shown in FIG. 45, the oxide films 32 are removed.Thereafter, mirror polishing of the surface is carried out to eliminateunevenness on the surface caused by the removal of the oxide films 32.In this way, as shown in FIG. 46, a super-junction semiconductorsubstrate is completed which has the first parallel p-n layer and thesecond parallel p-n layer. The first parallel p-n layer includes thefirst n-semiconductor layers 2 a of the n-epitaxial layer 31 and thefirst p-semiconductor layers 2 b of the p-epitaxial layer 34 c beingalternately arranged. The second parallel p-n layer includes the secondn-semiconductor layers 3 a of the n-epitaxial layer 31 and the secondp-semiconductor layers 3 b of the p-epitaxial layer 34 c beingalternately arranged.

With the use of the super-junction semiconductor substrate, the elementsurface structure, the peripheral voltage withstanding structure, thedrain electrode and the like of the MOSFET are formed at relatively hightemperatures, for example, of the order of 1000 to 1100° C. This causesinterdiffusion of impurities to complete the semiconductor deviceaccording to the ninth, eleventh, thirteenth and fifteenth embodiments.Since the processes of manufacturing the element surface structure, theperipheral voltage withstanding structure and the like of the MOSFET arewell-known, the explanation about them will be omitted.

The twenty-seventh embodiment is a method of manufacturing asemiconductor device which can be applied when manufacturing thesemiconductor device according to the above-explained second, fourth,sixth, eighth, tenth, twelve, fourteenth and sixteenth embodiments. Whenmanufacturing the semiconductor device according to the second, fourth,sixth or eighth embodiments, the manufacturing method according to thetwenty-fifth embodiment is applied. While, when manufacturing thesemiconductor device according to the tenth, twelfth, fourteenth andsixteenth embodiments, the manufacturing method according to thetwenty-fifth embodiment is applied.

In any of these cases, however, the twenty-seventh embodiment differsfrom the twenty-fifth and twenty-sixth embodiments in that the elementsurface structure, the peripheral voltage withstanding structure, thedrain electrode and the like of the MOSFET are formed at relatively lowtemperatures of the order of 400 to 800° C. With temperatures at suchlevels, interdiffusion of impurities due to heat history is inhibited.Hence, reduction in impurity concentration is prevented in each of thefirst n-semiconductor layer 2 a, the first p-semiconductor layer 2 b,the second n-semiconductor layer 3 a and the second p-semiconductorlayer 3 b. Therefore, compared with the twenty-fifth and twenty-sixthembodiments, the impurity concentration in the semiconductor device canbe easily controlled.

The inventors actually manufactured, according to the twenty-fifthembodiment, a super-junction semiconductor substrate as shown in FIG. 41with the impurity concentration in each of the substrate and the fillingepitaxial layers taken as 6.0×10¹⁵ cm⁻³. Thereafter, on thusmanufactured substrate, the inventors formed element surface structuresat temperatures of the order of 400 to 800° C. As a result, about thesecond parallel p-n layer, having the second p-semiconductor layers 3 bwith larger widths and laid out in a part of the inactive region 200,the impurity concentration in the second p-semiconductor layers 3 b wasabout 5.5×10¹⁵ cm⁻³. Moreover, the impurity concentration in the secondn-semiconductor layers 3 a was about 5.0×10¹⁵ cm⁻³. Both of the impurityconcentrations were uniformly distributed in the depth direction.

Furthermore, in the first parallel p-n layer laid out in the activeregion 100, both of the first p-semiconductor layer 2 b and the firstn-semiconductor layer 2 a have an impurity concentration of about5.5×10¹⁵ cm⁻³, which was uniformly distributed in the depth direction.Such impurity concentration distributions are approximately equal tothose in the second embodiment shown in FIG. 6 and FIG. 7.

Here, for making a well tradeoff between on-resistance and breakdownvoltage, when both of the first p-semiconductor 2 b and the firstn-semiconductor layer 2 a, formed in the first parallel p-n layer laidout in the active region 100, have a width of 5 μm, it is desirable forboth of the first p-semiconductor 2 b and the first n-semiconductorlayer 2 a to have a final impurity concentration of about 4.5×10¹⁵ cm⁻³.For providing the impurity concentration with such a value, it isnecessary only that the impurity concentration in the n-epitaxial layer31, which is to become the first n-semiconductor layer 2 a, is made tobe on the order of 5.0×10¹⁵ cm⁻³ when the layer is made grown. Moreover,it is necessary only that the p-epitaxial layer 34 a to become the firstp-semiconductor layer 2 b is made grown in the trenches 33 a and 33 bwith impurity concentration of the order of 5.0×10¹⁵ cm⁻³.

As a result of manufacture of the super-junction semiconductor substrateby carrying out epitaxial growth with such impurity concentrations, inthe second parallel p-n layer having the second p-semiconductor layers 3b with larger widths, the impurity concentration in the secondp-semiconductor layers 3 b and that in the second n-semiconductor layers3 a became about 4.5×10¹⁵ cm⁻³ and about 4.0×10¹⁵ cm⁻³, respectively.Moreover, in the first parallel p-n layer, both of the firstp-semiconductor layers 2 b and the first n-semiconductor layer 2 a aremade to have an impurity concentration of about 4.5×10¹⁵ cm⁻³.

In other words, there could be manufactured a semiconductor devicehaving the same structure and impurity concentrations as thesemiconductor device according to the second embodiment. Moreover,although the explanation is omitted, by changing the width and thespacing (pitch) of the trenches, a region having the width and thespacing of trenches different from those of the active region 100 (i.e.the region in which the second p-n layer is laid out) and the impurityconcentration in the epitaxial layers filling the trenches, asemiconductor device can be manufactured which has the same structureand impurity concentrations as the semiconductor device according to thefourth, sixth, eighth, tenth, twelfth, fourteenth and sixteenthembodiments.

The manufacturing method according to the twenty-seventh embodiment canbe also applied to when manufacturing the semiconductor device accordingto the eighteenth, twentieth, twenty-second and twenty-fourthembodiments. In this case, however, the manufacturing method of thetwenty-fifth embodiment is applied with the width of each of thetrenches 33 b, formed in the region where the second parallel p-n layeris laid out, made smaller than the width of each of the trenches 33 aformed in the region where the first parallel p-n layer is laid out.

In the foregoing, the invention is not limited to the above-describedembodiments but can be variously modified. For example, describednumerical values of dimensions of thicknesses and widths and impurityconcentrations are merely examples and the invention is not limited tothe numerical values. Moreover, on the parallel p-n layer, asemiconductor elements other than a MOSFET, such as an IGBT or a bipolartransistor, can be formed. In the above-described embodiments, the firstconductivity type and the second conductivity type are taken as ann-type and a p-type, respectively. The invention, however, is similarlyvalid even when the first conductivity type and the second conductivitytype are taken as a p-type and an n-type, respectively.

As explained in the foregoing, the invention is useful for a high-powersemiconductor device. In particular, the invention is suited for asemiconductor device in which breakdown voltage enhancement and currentcapacity enhancement can be compatible such as a MOSFET, an IGBT and abipolar transistor, each having a parallel p-n layer in a drift section.

1. A method of manufacturing a semiconductor device in which a parallelp-n layer with first conductivity type semiconductor layers and secondconductivity type semiconductor layers being alternately joined isprovided on a first conductivity type low resistance semiconductor layerand a part of the parallel p-n layer is provided over an active regionin which a current flows in a turned-on state and a part of the parallelp-n layer is provided over an inactive region around the active region,the method comprising: carrying out epitaxial growth of a firstconductivity type semiconductor layer on the first conductivity type lowresistance semiconductor layer; depositing an insulator film on thesurface of the epitaxially grown first conductivity type semiconductorlayer; carrying out patterning of the insulator film to form a mask forforming trenches; by using the patterned insulator film as a mask,forming a plurality of trenches in a region to become an active regionin the first conductivity type semiconductor layer and along with this,forming a plurality of trenches in a part of a region to become aninactive region in the first conductivity type semiconductor layer, thetrenches having widths different from those of the trenches formed inthe region to become the active region; carrying out epitaxial growth ofa second conductivity type semiconductor layer in each of the trenchesformed in the first conductivity type semiconductor layer to filltrenches having the largest widths with the second conductivity typesemiconductor layers to a level equal to or higher than the level of thesurface of the insulator film used as the mask for forming the trenches;and polishing the parallel p-n layer comprising the first conductivitytype semiconductor layers and the second conductivity type semiconductorlayers filling the trenches to planarize the surface of the parallel p-nlayer.
 2. The method of manufacturing a semiconductor device as claimedin claim 1 wherein, in the step of forming the trenches in the firstconductivity type semiconductor layer, in a part of the region to becomethe inactive region, the trenches are formed so that the width of eachof the trenches becomes larger than the spacing between the trenches. 3.The method of manufacturing a semiconductor device as claimed in claim 2wherein, in the step of forming the trenches in the first conductivitytype semiconductor layer, in a part of the region to become the inactiveregion, trenches having widths larger than those of the trenches formedin the region to become the active region are formed.
 4. The method ofmanufacturing a semiconductor device as claimed in claim 1 furthercomprising removing a part of each of the second conductivity typesemiconductor layers filling the trenches by an amount grown to a levelhigher than the surface of the insulator film used as a mask for formingthe trench by polishing the part with the insulator film further used asa polishing stopper, the step being carried out between the step ofcarrying out epitaxial growth of the second conductivity typesemiconductor layer to fill each of the trenches and the step ofpolishing the parallel p-n layer to planarize the surface thereof.